As for 1st point, check out section "Pure Android". It says you shouldn't copy UI style from other platforms. I think this could be extended to major versions o

As for 1st point, check out section "Pure Android". It says you shouldn't copy UI style from other platforms. I think this could be extended to major versions of single platform too. App with Holo theme on Froyo phone would look very out of the place, I think.