The top reason I'd think of? Most companies build the iOS version first then port it to other platforms. That's usually under tighter deadlines than the iOS version had and there's not much design flexibility. Just make it work almost identical to the iOS version and it needs to be done tomorrow.

It is funny to hear that rounded rects are still an issue in 2012. http://www.folklore.org/StoryView.py?story=Round_Rects_Are_E...