Few Android users keep the default backgrounds so it's only natural for Google to change too. It also makes it easy to see that it's new and different.
I find the 5 year old iOS UI boring and much less usable than the AOSP Android UI.
And this could be related to the fact that the Android team is refining the UI with every iteration.
Check out some geocities sites from a while ago for some 'usable' websites.
Personally I feel like the UI of iOS is very aged, requiring you to click on a icon to see information about that app whereas a widget allows a wealth of information at a glance. Often even access to an application's controls without having to open the app.