I think sexualization does work well for marketting and I do think that it sells. However usually a game needs to have more than just sex appeal to sell it to me, Ashley's sideboob and pixelated arse alone did not sell me on Mass Effect at least. The great setting, universe, story and characters did that.
Also while I'll agree that sexualization DOES help sell games, that doesn't mean I approve of it and I also want to draw attention to say, the Halo franchise which is a multi-million dollar juggernaut that from one little X-box game became a media empire with books, toys, comics, video game spinoffs, anime, tshirts and a possible movie in the works. Never once did it have to 'rely' on sex appeal to market or sell itself. Granted Cortana is about as hot as computer software can be but even in trailers where she's prominently featured she's never sexualized on screen nor used as a 'selling point' in the same way other female characters are.
That's the thing, as far as I'm concerned sex does sell but it doesn't mean companies have to rely on it to sell. Frankly for the most part when I see games, or most things, that use sex to sell, especially if sex appeal isn't even a feature of the game/thing in question, that's when I get annoyed.