Tricky, but not impossible. The same as you would have to learn the API's and general usage patterns of new features, you just have to learn how to use the compatibility package or third party libraries like ActionBarSherlock to take advantage of the most common new features.
That said, I don't fully agree with the OP's argument. Fragmentation is a very real pain in a lot of subtle unexpected areas (mostly UI related).
I think that he means that it is tricky. He doesn't hide this fact, but it is a know fact, and programmers should be award of it and its possible solutions.
That said, I don't fully agree with the OP's argument. Fragmentation is a very real pain in a lot of subtle unexpected areas (mostly UI related).