look at it like this...people of color ask those questions...who is the best black qb ever because traditionally blacks weren't allowed to be qb's. when people say who is the best rb ever....jim brown, walter payton, emmitt smith, barry sanders..these guys usually are the ones mentioned. notice they are all black...i know a lot of white people that will ask the question...who is the best white running back ever? they do this because it makes you think...there weren't alot of GREAT white running backs(when compared to the ones we already mentioned).
yes it would be great if we could be color blind and just say who is the greatest qb ever, but what you have to understand is that there were so many black qb's that never got a shot at playing qb BECAUSE they were black that some guys that might have been as good as the marino's and montana's were overlooked.
also when growing up you want to be like some one who you look like. i didn't want to be larry bird, babe ruth, or dan marino...they're white, they don't look like me. i want to root for someone who looks like me, someone that i can identify with. i went into the yard and i was pretending to be barry sanders, mike jordan, jerry rice, ken houston, deion sanders, hank aaron...people who look like me. people want to know about people who look like them so when people talk about great players they can talk about someone who looks like them..ie one of my good friends was a hispanic ol(6-2 290), and was one hell of a linemen at that. he favorite player....yup you guessed it munoz from the bengals. when we talked about great players he always threw up munoz...he wanted to stand behind a guy that came from his heritage...THAT is why people have the conversations of who is the best asian, black, white, hispanic, somoan, etc player.