As of now I believe Clemens (not 100 percent though) for one thing he has done differently than other big name potential steroid users (McGwire, Sosa, Bonds, etc.).
Most of the players have publically denied use, evaded questions, some have even threatened lawsuits. However, Roger has taken the onus on himself, and has said he will take a lie detector test and I believe he is trying to prove he is innocent not only by showing the loopholes in others stories (as many players have), but proving it by himself. Also, he would have to be rather dumb to go this far and actually have taken steroids.
And for those who say that he evaded questions in his press conference, he had to has a lawsuit with his trainer coming up, and couldn't tamper with the case.