One of the things I really used my iPad for a lot is games. The distribution mechanism and purchasing system are super-simple. You could (and can) get high-quality games for a low price. I see I've spent 100+ hours playing Bejeweled 3 alone.
Yet the trend has clearly gone towards in-app purchases. I tried some golf game (Tiger Woods something?) and it was constant nagging for in-app purchases. That got deleted in about 2 minutes.
Then there are the "social games", which to me is really an abuse of the word "game", since they are nothing more (IMHO) than exercises in feeding addiction and inducing compulsive behaviour. There is no element of skill. It's simply who can purchase the most. And I've tried a bunch (spending no real $$$) to see (I'm a sucker for world-building games and there's a dearth of those, sadly).
The second category (normal games with in-app purchases) create the wrong incentives. Whereas Angry Birds originally spread because it was a hugely fun game, the game developer is incentivized to make you fork over more money, typically at the expense of the game itself.
It saddens me that Angry Birds has gone the in-app purchase route too.
Sadly the genie is out of the bottle. Any sensible game developer will go this route. Add to this the "social" layer being foisted on users and it's really looking like dark days ahead for gaming.