Some interesting research to be done
In discussions with a few psychology experts, there appears to be some interesting dynamics involved with nudity and attraction. Men like looking at (attractive) naked women. Women like looking at (attractive) naked men. Women also like looking at other women. Men, however, fall into two groups. For most of us, there is a built-in 'threat response' involved with the view of a naked man. This has been demonstrated by fMRIs in several studies. The second (smaller) group of men lack this threat response and may also find another naked man attractive. This group may correspond with Kinsey's research showing a (startlingly) significant minority of men that have some level of attraction towards other men. Even those that identified themselves as straight. Kinsey found this to be about 35%.
From the point of view of 'acceptable' naked images (avatars, game figures, etc.) it would seem that, given an unknown audience, the naked female form offers the least chance of triggering a negative subliminal response. With naked male figures, that possibility increases.
The interesting research would be to strap a cross section of the population into an fMRI and compare their responses to their answers to Kinsey's survey and other issues of sexual identity. It may turn out that the lack of this threat response trigger is genetic. And it might be a necessary, although not sufficient condition for bisexuality or homosexuality. It might also be tough to do, as many gays don't like being poked and prodded (scientifically, that is) as if they suffer from a disease.