I just found an article talking about the difference in UI on iPhone and Android phones at the Android Gripes blog called “Why do apps from the same company look worse on Android than on iPhone?”
The examples show different apps, amongst them the iPhone and Android version of Facebook. The question asked at the end is more or less why is it so?
The answer to this questions lay in the point that when you design for iPhone you have a fixed screen aspect ratio you design apps for. It is a “controlled” environment and you know what phone user has, and it will look the same on all iPhone’s. For Android phones, UI designers must (for the most cases) take in count all the different versions of Android phones, with different form factors and screen resolutions when they design their interfaces.
Because of that, the interface then need to be designed more flexible and that comes with an extra cost of time/money and effort. Either you design different UI’s for different form factors and screen resolutions, or you create a UI that uses features that work 80% good on a lot of devices.