I'll go on record stating that I am one of the rare few who actually like Avalanche's cover art. There's three reasons basically:
1. I'm a guy, the rest should be obvious...
2. It harkens back a bit to the early days of the RPG hobby, when publishers really had no intention of marketing to women (since women weren't seen as a viable market). Lots of covers and interior art 'back in the day' featured similar themes (half naked womenfolk). Even looking back at the art inside early AD&D books such as the Monster Manual 1e you'll see cheesecake and even -gasp- nekkid boobies.
3. To me at least, it reflects on the attitude of the design companies. Avalanche's cover art, when I see it on a store shelf, says to me 'hey, we don't take ourselves too seriously, it's a game, we're having fun'. Compared to the self absorbed and often shameless seriousness and trend-riding seen in the attitude of other publishers, I find this very refreshing.
And to top it off, I've gamed with quite a few women in my time (22 years now, god I feel old), and have yet to meet one who took serious offense to the art in the books. I realize there are women who do, and have no issue with that, but to me the solution is obvious. If you don't like it, don't buy it, if enough people 'protest with their wallet' in such a way, Avalanche (or any publisher for that matter) will get the point and the offensive material will go away. To me, the endless ranting and poking fun on the internet about such things is rather pointless. Avalanche is still around and still selling the same type of product identity, so obviously they feel it's working for them financially.