[Dominic]

it does seem to be a mix between "nurture vs. nature." I, too, know straight men who talk like this, as well as plenty of gay men who don't.

It does seem to me to be a way of "belonging" to a community of some sort for some of the more flamboyantly lisping gay men. Obviously then, it's an affectation for these people.

but what about the straight or gay men in middle America who talk like this, without having access to a socially acceptable "gay" community/bar/whatever? Where does this speech patter come from?

I think it's pretty perplexing, but those article you linked were interesting.