That black quarterbacks have a fairly low success rate? Griffin isn't Mike Vick or Vince Young. He's a FAR better passer, and WAY smarter than both of those guys put together. He's not an athlete who plays quarterback. He's a quarterback who's an athlete.
I don't know what that posters reasoning is but I've heard his height has been a bit of a concern for teams (when I say bit, I literally mean bit as he's still easily a top 5 pick)