Federer has a harder time returning Nadal's serve in contrast to Roddick, for the obvious reasons..........Roddick's placement is in almost the same exact spots each and every time with the occasional body serve......at least with Nadal he'll go for the line, the middle, or out wide. As simple as that.
Olderer has huge problems with low pace serve with extreme spin to backhand.
Duck's serve hardly carry any spin and are all pace and predictable at that. Thus, he finds all his serves blocked back at him and the rally starts at neutral on almost every point. Federer vs Roddick in a rally, we all know who will win those.
The only anomaly was Wimbledon, where Olderer was outplayed in rallies, but literally served Duck off court. Hit something like 50 aces, ridiculous stuff.