There's productivity apps though. You SHOULD be able to find almost anything you need for all iOS, Android and Windows Phone at this point, but the quality differs widely.
On tablets, you have Penultimate for iOS for example. I'm an android user. We have semi-equivalent apps, but none are as good.
Exchange support: On Android, the best one is Touchdown. It works, but it looks like crap, and drains battery like crazy. The Windows Phone support is better (amusingly enough, not as good as Windows Mobile was though).
For scanning documents when i dont have a scanner handy, I use CamScanner. Windows Phone has similar applications, but none are as good. I don't know if iOS has better or not. Probably does.
And for games (do keep in mind that the vast majority of people with smartphones use them outside of work), iOS is king, as virtually all games available for other platforms will have an iOS implementation, but the other way around is often not true. All platforms have Angry Birds, but.....ugh.
Thats just a few examples, but its really important: you have the basics on all platforms, but the "bests" are often not cross platform.