I read an article in Baseball Digest 20+ years ago. The writer suggested that Babe Ruth should have an asterisk next to his home run record, not Roger Maris. His reasoning (if I remember correctly) was that most of the pitchers that the Babe hit his HR's off of would not even have made it to the majors in 1961. He listed all the pitchers and I think some stat's.
I believe that is true, while there certainly were some great pitchers back then, most would not make it to AAA in today's game.
I did a quick google search, here's the list:
http://www.baseball-almanac.com/feats/feats12c.shtml
Dan