In both lists, George seems to pay as much attention to what the fighter did in terms of expanding some aspect of the sport as to his ranking in terms of H2H or P4P ring ability. By this I mean, he takes into account the symbolism of Jack Dempsey and John L. Sullivan as cultural icons to the masses, the importance of Ali as a cultural icon to black Americans, the achievement of Rocky Marciano in forever after being the first undefeated champion, the achievement of Floyd Patterson in being the first heavyweight to regain the title, etc. etc. He includes elements of historical perspective into his ratings which seem to be in his mind just as important as ring ability.
Foreman would add this follow-up comment: "The first 2, there is no room for argument! But the others can be moved around anyway you feel. Lewis could be anywhere; Ali, Holyfield are solid. Holmes had the best Jab, Liston and Frazier were my favorites." Ali and Frazier both highly respected Louis and Marciano and have them as top HWs, they are 1 and 2 for Frazier as well. It has more to do with the era you saw while growing up.