Other than the trip back to the U.S. from Thailand, I can't see that he's been treated like royalty.
I heard analysis of the Thailand trip on one of the news programs that made some sense. It was easiest for those in charge of watching him to do so in business class. Once there, Karr was fed what others in business class were being fed. They weren't going to send out to McDonalds to get him something else. The one thing that I question is allowing him to have alcohol, since even if he "opened up" and started talking, whatever he said would certainly come under fire later once he got a good defense attorney (assuming that ever happens).
But once on American soil, how has he been treated like royalty? He's sitting in a cell like any other prisoner. It's the media, and it's us, that's creating the circus. Blame us, and blame our endless thirst for details about the case.