One sure fire way to get a bunch of tech geeks into a heated war of words is to take sides as to which is superior iPhone, Android, or [cough] Blackberry. Nothing gets a lively conversation started faster. That being said results from Mplayit on Facebook found that regardless of which horse we back in this race, we end up using the same apps no matter what. As it seems, Angry Birds and Facebook are that compelling to everyone.
The tidbit that should be extracted here is that it underscores the necessity to know your audience and know them well. If we know users will use the same apps cross platforms then this is as solid of proof as any that exploring all three platforms may be worth your while.
Another tidbit here is that it shows a high chance of success from one platform to the next. If you hit one out of the park on Android, chances are in your favor of repeating that on iPhone.