I know it's easy to say that now, it's part of what makes it funny, no one could have guessed how different their carreer would turn out to be. Still even though they were pretty much equal in the accomplishment category, it was clear that Roger had superior talent and much more variety. Something that JMAC was very much aware of and kept mentioning, it was just the intro that was a little bit over the top
If I remember that match really signaled Federer's entry onto the big stage. He'd had a couple tournament wins, and had beaten Sampras a couple years ago on Centre Court. But that was his resume at the time. Roddick on the other hand had won a grand slam, been #1 in the world and was clearly at his peak or even possibly still rising (speaking from the perspective at the time).
McEnroe had first mentioned Federer as a possible GS champion in '99. At that time ('99) and in 2003 he was still the guy with so much potential who hadn't quite learned how to harness all that talent. His was, to that point, a somewhat dissapointing career.
My point is, they were not equal in accomplishments. At that time in tennis, Roddick was clearly the "star" and Federer the upstart.