By comparison, Sony's PSP system only has an audience of around 18 million, and Nintendo's DS audience in the States sits at 41 million. We've talked about sales of all of those systems before, but the same survey says that while two-thirds of gamers will pay for games on traditional handhelds, a much smaller percentage will pay for games on the iDevices (only 45% on iPhone and iPod touch, and only 32% on iPad).
Not that apps aren't bringing money in -- Parks Associates also says that the North American apps market is now worth $2 billion, and will double in value over the next few years. Even if gamers aren't willing to buy games, more and more are willing to put up with ads in both games and apps -- a recent report says 45% of adults 18-34 don't mind sitting through ads to play games and use apps for free.
In short, Apple has built one heck of a market here in the last few years, and it's only going to be growing from here on out.
Apple iPad Air 2
Apple iPhone 6s
Sony PlayStation Portable PSP-2000