@Trickquestion  
For more reasons than one.

@Scrounge  
I really like the idea in concept, but if they dropped it into the show now, after four seasons of Celestia barely interacting with Spike while lavishing praise and affection on her not-daughter Twilight it’d be really messed up.

@Trickquestion  
Yeah, it’s all kinds of messed up. I’m not sure there’s a word for what’s going on with them, honestly.
 
Nothing on the show ever gave me the impression that she was ever his substitute mom the way Twilight is. He certainly doesn’t seem to be anywhere near as close to Celestia as he is to Twilight (or as Twilight is to Celestia, for that matter). So I think you’re safe.

@Scrounge  
I’m not sure Stockholm Syndrome is the right word, but whatever Spike and Twi have going on is some kind of psychologically unhealthy.
 
I actually really hope Lauren’s statement about Celestia raising him isn’t true.

@Trickquestion  
I think his life would have improved if Applejack hadn’t given him back.
 
Then again he might just have Stockholm syndrome for Twilight at this point.

@hironakamura  
As Trickquestion said, D&D dragons tend to be absurdly powerful in a bunch of different directions. I’ve actually never seen their take on dragons used by anything that isn’t directly inspired by the game, and while MLP can come across as a table top game, it’s never treated it’s dragons like that.
 
Basically, people are more likely to draw inspiration from Tolkien than from D&D when it comes to dragons.

@hironakamura  
In Dungeons and Dragons, two types exist: Chromatic and Metallic. Chromatics are ruled by the five headed, Chaotic Evil engine of destruction Tiamat, and metallics by the Lawful Good Bahamut (that’s not the right spelling, but that’s how’d you’d say it phonetically). Chromatic dragons have one breath weapon based on their scale color (red and black breath fire, yellow breathes lightning, white breathes cold, etc.) and Metallics get two breath weapons, though which color gets what I’m not totally sure on. Both types are immensely powerful spellcasters and posses genius level intelligence, and they’ll basically live forever if they can keep eating and growing. Not through hoarding though, that was something FiM made up. The reason DnD dragons hoard are a bit different. In addition to using the money to fund their often century spanning plans (among their many magical powers is shape changing, allowing them to walk amongst humans) the main reason dragons hoard is to collect magic items. They end up with a lot of none magic junk as a bonus, but the stuff they’re really interested in is the magic equipment.

I don’t think dragons have kingdoms or structured societies like the ponies do in the MLP universe despite being one of the intelligent races.
 
Based on the red and green adult dragons we’ve seen in S1, all they seem to do is accumulate stuff and guard it. That would also make sense if they are magical creatures of greed. I don’t think two or more dragons would “share” the same hoard. The migration would also make sense. Most things that migrate usually do that to mate.
 
My guess is Spike’s egg was abandoned not out of cruelty or that his parents were killed. I think it was normal for dragons to do that. Spike’s egg might’ve hatched by itself and then he would have raised and taken care of himself in the wild with nothing but instinct like most lizard young do. But that wasn’t Spike’s destiny. His egg was meant to be found by ponies.
 
Then again its canon that ponies know next to nothing about dragons. They are intelligent and potentially ancient. How are dragons depicted in DnD universe? MLP has a track record of drawing inspiration from DnD.

@Background Pony
 
Sorry Batman, but not all of us have a really large mansion on a hill and pretty much owns an entire city.

“Do you know who else had no parents?” Batman.

@Trickquestion  
Agreed. That’s why I can’t wrap my head around stories like “Past Sins” where Twilight is suddenly a great mother. She’s already done a lousy job at being a parent to the child who is already in her care…

@Background Pony  
That…  
Wasn’t so bad…

@HJSDGCE  
Okay, time for my twisted Spike headcanon. Bear with me here:
 
Spike is actually an adult dragon. He doesn’t realize it, though, and neither does anyone else, because he’s under the influence of an Age spell (the magic Trixie used to change Snips and Snails into babies during “Magic Duel”).
 
What happened was this: Long ago, Celestia came into possession of a dragon’s egg, how is anyone’s guess. She cast an Age spell on it to keep it from hatching, with the idea that it’d be a test for any Unicorn who could become a threat to her rule. If a Unicorn could nullify the Age spell and hatch the egg, that Unicorn would have power that could rival hers.
 
Years passed, and along comes Twilight Sparkle in “The Cutie Mark Chronicles”. And not only does she nullify the Age spell on the egg, she dispels it completely, causing Spike to revert to his “natural” age–the age he would be if Celestia hadn’t enchanted his egg to begin with. This is why Spike went from hatchling to full-grown dragon in seconds. Celestia intervened and recast the Age spell, dialing Spike down to a hatchling to cover her tracks.
 
The second time Spike grew to adulthood, in “Secret of My Excess”, his native dragon greed was aggravated and began to fight the effects of the Age spell, causing him to start to grow. Zecora’s theory that greed was causing him to age was only partly right–the greed wasn’t causing him to age, it was causing the Age spell on him to weaken. The spell was almost completely worn off when Rarity came on the scene. Spike’s love for Rarity tempered his greed, which caused the Age spell to start working again and reverted him back to his baby dragon form.
 
How long Spike is going to remain a baby dragon is probably one of Celestia’s secret schemes. Maybe when Twilight learns enough magic to cast an Age spell herself, she can lift the spell off of Spike and allow him to become an adult if he wants.

@AaronMk  
I did not get anything from that.

@HJSDGCE
 
Does this mean that Twilight is…
 

What if, Spike’s egg was actually a well decorated stone that measures magic energy inflicted on it, but when Twilight used too much magic on it, it became a hatched dragon’s egg.
 
In short, Twilight made a dragon egg from a rock.  
Shorter, she made life.

Actually, it’s worse. You have a parent, but she’s terribly negligent and totally unskilled at nurturing.

@Itsthinking  
Something quick and violent seems most likely. Whatever kind of society exists, Spike is old enough that he doesn’t need adult supervision, given how the green adult was willing to handle him, and how none of the adults thought that it was noteworthy that he arrived at the migration by himself.
 
We’re not looking at cities or senates, is what I’m saying, and even clans are probably unlikely.

@Alel  
Runs into the fact that Spike is the only dragon in pony society.
 
If other ponies were hatching them, there’d be more information on dragons. Unless the other eggs didn’t have dragons in them…

@Sjogre  
So a bit of what dragons do may in fact just be a result of their society, whatever kind it exists.

@Itsthinking  
Something to think about… Spike is the only dragon we’ve seen with a response other than violence. Okay, the red adult ignored the manes for a bit, but it still went to violence under far less provocation than it took to get Spike to use non-lethal force.
 
He’s also the only pony-raised dragon that we know of.

The eggs used in the pony magic school were created with pony magic and could only hatch with pony magic. Hence the test.

@Ertinax  
Yeah, but imagine growing up in a species that does…

@Itsthinking  
They’ve only been shown speaking the same language as the ponies, and fighting is no evidence of civilization.
 
Technically, found in an abandoned horde would also fit as option D, but I wanted to make it clear that it wasn’t deliberate on the part of the parent.

Or dragons, like a lot of species, just don’t care for their young.