Well, a UI is just that...a UI. That's why there are soooo many launchers on the Android platform.
However I do agree that it only makes sense to get a WP7 phone if you like Metro so much.
However, Android is a more mature platform with a lot of the growing pains already taken care of. WP7 still has some maturing to do.
Yeah, its mature in way of hundreds of thousands of apps. You would think that in this maturing, they would have freshened up their UI. Instead they wait until the next best thing comes out and they try to copy it. Google has already admitted that they have a problem innovating. The fact that their users and developers are trying this proves it. Thats why there is a big shake up going on internally at Google.