Excellent, excellent points, guys. I am struck, first and foremost, by the fact that there has been virtually no discussion of the fact that two of our greatest made the NFL's top 8 all-time. I, too, am struck by the fact that Doug Atkins did not make the list. Particularly during the first half of his NFL career (1950s), he was an absolute "freak of nature" in terms of size and strength, and an utterly dominating force on the defensive line.
As for the "old, white guys" argument, I would like to raise two points for further discussion. First of all, these guys played in an era when most coaches were adamantly opposed to regimented strength training, based on the archaic premise that it would make them "musclebound." Second, there is no question that the overall trajectory in athletic performance has been in the direction of bigger, faster, and stronger athletes. The one timeless measure of greatness is not how such and such player would fare against today's competition but, rather, to what extent did he surpass the accomplishments of his peers.
For those of you who would argue for Barry Sanders or Walter Payton over Jim Brown, I would grant that your position is thoroughly defensible, but how many of you actually saw Jim Brown play? His achievements towered over those of his peers to a far greater extent than any running back who has succeeded him. Brown led the NFL in rushing eight of his nine seasons, he was the first 1,500 yd. rusher (in 12 games, 1958), the first 1,800 yd. rusher (in 14 games, 1963) and he eclipsed 1,400 yds. in five of his nine seasons, all without ever having the benefit of playing in a 16-game schedule.