You do realize that aesthetic appeal doesn't exclusively mean sex appeal, right?
We have to make characters in some way aesthetically appealing because that's how you generate empathy. This is just rooted deep down in human psychology and there's little that can be done about it: pretty people are more sympathetic than ugly people, and that will always have an influence on how characters are designed and (in film and TV) cast. That does not mean that the only motivator for feeling empathy is sexual desire.
That doesn't mean it's incredibly important, ultimately. Legend of Zelda would still be fun if Zelda and Link were representative of "real women" and "real men", I'd just prefer they not be. Living up to ideals is central to the appeal of fantasy.
Continuing with that example, would it be reasonable for me to expect that, when I was a teenager, I'd just for granted have this obnoxiously cute quasi-romantic relationship with a hot blonde and that a central component to this relationship would be fending off douchey classmates and, heaven forbid, saving her from the literal embodiment of evil (going off Skyward Sword here, if not obvious)? Heck no. That doesn't happen in the real world, but no one would want to play the game if the relationship between Link and Zelda was like that of most teenage couples, ie approximately 8 months of boring dates, clumsy groping, and awkward sexual tension. It's not just Zelda's appearance that has been idealized but also the drama of the story.
Ultimately, I really think it's down to the Law of Conservation of Detail (http://tvtropes.org/pmwiki/pmwiki.php/Main/TheLawOfConservationOfDetail) Details are not included in the story unless they're somehow important or relevant. If the character is fat, or otherwise has a "non-ideal" body, there has to be a reason. Otherwise, conservation of detail demands you default to the ideal.
What this does not mean, and here is where I strongly disagree with OP, is that the only appeal that can be invoked is sexual in nature. Building a game around sex appeal is antithetical to generating good fantasy, it does in some ways exclude a female audience (women typically are not sexually interested in other women), and it perpetuates the stereotype of gamers as being sexually frustrated frustrated man-boys who never fully overcame their fear of cooties which, honestly, the behavior of some gamers isn't helping with either.
Social issues aside, let's just talk about how to market to a female audience. What must be understood is that character designs like Bayonnetta and Lara Croft (yes, even the new one), are male fantasies. Male fantasies do not appeal to women. If men are your target demographic, then fine. But women make up half of the population, and they're not buying video games. It's stupid to not try to access that market. In large part this means developers need to work to eliminate the "frustrated man-boys" stereotype. Practically speaking, that will mean that the focus might need to shift away from sex appeal to gain broader market interest.
That absolutely does not mean that female video game characters all need to be replaced with "real women" with "curves" and body hair. Aesthetically appealing female characters are important to women as well: look at the cast of, say, Pretty Little Liars. Aesthetic appeal will always be important in general for marketing. But sex appeal is gender-specific, so it doesn't make for a great strategy to generate broad popular interest.
