Then how do you explain a Byron Leftwich or a Doug Williams? You are correct in general, but not in total. While in general, a quote like "White Men can't jump" is correct, many white men can jump higher than equally sized men of other races.
Making overreaching statements like you did is either acceptable or it is racist. Which is it? Most white males want to know, since we are allowed to be denigrated by generalities, yet cannot make similiar statements about others. For some reason, it is acceptable to give Asians credit for being smarter, but not African Americans for being more athletic.