Put Bolt up against all other 6'5" athletes and he'll blow them out of the water by a much bigger margin than Johnson was able to beat people his size. That's what makes Bolt so unique.
Yes, his height and stride gives him an advantage, but nobody in the history of track and field has ever been able to use that to overcome the disadvantages of added air resistance and mass.
BTW, have you ever seen Donovan Bailey's 100m run in Atlanta? After the first 10-20m he was at the very back and a couple metres behind the leader. That he was able to break the record after that terrible start shows how fast he went. Most sources cite his top speed as 12.1 m/s in that race. Bolt's was about the same (
0.82s per 10m = 12.2 m/s), but he had a great start.
Michael Johnson's record was amazing in that nobody could get near it for over a decade, but given that Bolt himself didn't get close before Beijing makes this run just as great. It will be fun watching him for the next decade.