You did a good job of selecting your examples, but here goes:
Tiger & Kobe: The biggest stars in their sports. Tiger, by FAR the biggest star in his. So, they're bigger stories.
McGwire/Clemens/Bonds: First, McGwire avoided the question, but did not lie. Second, Clemens hasn't escaped trouble yet. Third, Bonds is a prize a88hole, and sometimes that comes back to bite you. (So is Clemens, which probably is why he hasn't escaped trouble yet.)
Here's some counterexamples: the Duke lacrosse players versus Michael Irvin. Jesse Jackson versus Jim Bakker or Gary Hart. Craig MacTavish versus Leonard Little or Donte Stallworth.
It's not always about race. With sports, especially, I think the field is more level, compared to other areas of endeavor.