Agree, Roddick's service power and spin is more a function of his incredible leg propulsion more than anything else. His secret is that he loads his legs up, and uses them to propel the rest of his service motion like no other before. He gives himself a marvelous platform to push off from in other words, other than that his biomechanics are pretty standard and sound, just with a whole lot more racket head speed is all.
With that said, anyone can have shoulder problems at the pro level after a few years, regardless of their motion.
I mean it's like how any NBA player can have problems with his knees after a few years. I mean what do you expect? Basketball players jump a lot, and tennis players serve a lot...and baseball pitchers pitch a lot.
It doesn't always mean that the way one plays a sport is the reason for those injuries, it could factor in certainly, but the main factor is simply that one plays a sport every day for hours on end. From that perspective, Andy Roddick is quite normal among professional tennis players...he serves a lot of balls. If that eventually leads to shoulder problems, that might just be the luck of the draw.