I don't know what statistics say, but I wouldn't be surprised if service-related statistics favour Roddick.
Because players with absolutely great serves there have been dozens in every decade, and most of them never even reach a GS final.
And all these players with great serves (Forget, Wheaton, Stich, Krajicek, Ivanisevic, Rosset, Larsson, Arthurs, Johansson, Philippoussis, Isner, Karlovic...), they may have some (or many) service-related statistics with better numbers than those of Sampras or Roddick. I would not be surprise if that were the case.
Why? Because you don't win many GS tournaments and be nš1 in the world for years because of a great serve (as I said, most of the great servers of each era don't won GS tournaments, don't even reached GS finals most of them, even if they win almost as much service-games as Roddick or Sampras).
It is the whole package that is important, and it shows most in the return-games.
It is possible that Sampras won many more return-games than the rest of those great serve players (even though Sampras usually never tried hard for a second break of serve if he was already up a break).