I think it also depends on use. I had a 60cm frame, when I usually ride a 58. I barely touched with stand-over. City riding, a car ran a light, slipped on a pedal, and contact with the top tube. Wouldn't want to experience that again.

I do think some room for standover is a good idea. If you're riding a frame where you do not clear the top tube - hate to say it, but it's a matter of time/luck.