No, this is right. A zero-sum game is where there’s a fixed pot of money, and when one pony makes money, the amount of money left for the other ponies becomes smaller.
 
Gambling is a zero-sum game. The only money available is the money the gamblers bring in. When the house wins, the amount of money the gamblers, as a whole, can bring back out is less than they amount the gamblers, as a whole, brought in. (Usually by a lot – none of those billion-bit casinos was ever built on the gamblers’ winnings.) Individual gamblers may go home with many times more than they brought in. But that also only means the majority of gamblers went home with much less than they brought in. It cannot be any other way. Money lost into the system(-) + money taken back out of the system(+) = 0. Zero sum.
 
Mining is not a zero-sum game. You can bring in money to buy digging equipment, but after digging you could come out with ores that are worth more than the cash you brought in. At the end of the venture, the money you spent on digging equipment is still there (in the hooves of the equipment maker) and you have new money that didn’t exist before you dug up the ore to back that new money. Agriculture similarly creates new value by turning sunlight and air into food energy. At the end of the transaction, the total amount of money in the system is higher than before the transaction.

@donut64s  
but what do we know? Pinkie (and Equestria) may think differently.

IT does not seem so that this is, in real life, a zero-sum scenario.

lol awesome comic cool XP

@TwilightVelvetSparkle  
Going off this comic, I’m pretty sure that’s the joke.

Just going off wiki, pretty sure that’s not a zero-sum game. A zero-sum game is where the participant(s) are neither winning nor losing. In the situation described, there is a clear winner and loser; the loser is the one playing the machines, the winner is the owner/machine (usually). Even if the player does not achieve a higher total than when they initially played, they still reach an amount not possible without playing if they even when once.
 
I could be wrong though; not an economic major or anything.