I've always thought that Blake had more clay court game than Roddick. His weak serve is not as big an issue on the surface, and being fast and having a huge forehand are going to help you regardless of what you're playing on. Of course, Roddick does have all the Houston titles so...I don't know.
In any case it's great to see Blake getting good results on the dirt.
"Everybody has a game plan, until they get punched in the face" -Mike Tyson