For a while it was a pain when a game forced me to choose between an iPad version and an iPhone version. More often than not there is a universal iOS app now that supports both platforms.
However, my frustration kicks in when game state cannot be synchronized between iPhone and iPad. I am still in the scenario where I have to pick which platform I want to play the game on, and not be able to switch between devices.
Not all games are like this though. In fact I have a couple games that work between iOS devices, including our Apple TV.
My wish for game developers, when creating a universal app, would be to put some time and effort into supporting iCloud based data so that players can switch between devices seemlessly.