Women just aren't that hot anymore. Present company excepted.
Honestly? I think that they were so hot because you never totally saw them in the all together. Nowdays every actress around has done some sort of Playboy spread or semi-nude photo shoot for GQ or maxim or whatever...and a man's imagination is sometimes better than the real thing.
I think people like Jane Russell and Betty Grable and Lana Turner and Rita Hayworth are hotter because of what they hinted at, but never showed...