Attempting to see all this from as wide a perspective as possible, I think it's only natural given the incredibly fast pace at which mobile is developing right now. The mobile industry is in the middle of a massive renaissance, Apple somehow ended up right at the center of it, and it just makes sense to focus all their resources on it while they have the advantage.

In a few more years, as this new generation of mobile matures, Apple will probably shift back to the desktop as the pieces begin to drift together for the next generation there.