Federer doesn't cross behind often when he's moving to a standard forehand or backhand... Instead, he uses a variation where he takes a shuffle step immediately after the split step. It actually looks like he's taking two split steps because the footwork is virtually identical. You can see what I'm talking about in this point (which many of you have seen):
http://www.youtube.com/watch?v=9tZhQi8aDcg
The benefits are the same as the cross step. For example, he's giving himself some time to judge the ball before he fully commits. On a number of the backhands he hits he'll shuffle and step in vs immediately moving forward coming out of his split step.
I'm pretty sure I mentioned that Federer uses this alternative in the footwork video when Yann is talking about the cross step... Although we re-shot a few segments so maybe it didn't make it into the final version.
Here's Rafa using the cross step to get to his backhand:
http://www.youtube.com/watch?v=iTpRr_1r0aE#t=1m33s
As JR pointed out earlier, his left leg comes in line w/his right leg vs crossing over completely. That's just fine -- still a cross step.
Finally, both Fed and Rafa use the cross step all the time to move to inside-out / inside-in forehands.