I-mockery said it best about comic book cover cliches
This one should be obvious: a cover depicting some scantily-clad heroic or villainous vixen, and not much else. A book like this just screams "No substance to be found here!" but this is also the type of thing that horny 12-year old boys buy up like hotcakes. I know, because I was once a horny 12-year old boy, and I bought a lot of these comics. I did not, however, buy up a lot of hotcakes now that I think about it, so perhaps that analogy doesn't hold up. Regardless, these books always seem to do fairly well, although they're not as popular or prevalent now as they seemed to be in the 90s, when they got absolutely out of control and seemed to account for about half the shelf. Hell, Image and Marvel even used to do swimsuit specials, and that's pretty damned scary.
While you have a point Ziffy88, I think you have also forgot something important. The writer. It's not the writer who writes (at least, not usually in my experience) that all female characters have to look like women from Baywatch (showing my age here, better watch out), it's the artist. Now, this certainly doesn't apply to everything, but look at the number of classics from the time period you mention and look at their art; you're right they are under dressed significantly, but are they poorly written?
That depends on who was doing the writing for that comic at the time. I've seen some that were a waste of time and others that had good plots regardless of what the artwork did, and that's the same way it is today.
For me, the story sells me into the comic, not the art. For me the art always comes a close second.
Of course this is a moot point with webcomics since the writer is usually the artist as well.