[flippant second paragraph redacted so I don't have to explain that he's not actually a fucker]
I think in some ways it makes sense for members of sexual minorities to coalition together. In some ways, including asexuals arguably makes MORE sense than including transgender folks -- since gender identity/expression and sexual orientation are very different issues (though they certainly have overlap).
Of course, there is the problem of diluting the "queer" label ("queer" being my preferred term for the GLBTetc. umbrella) -- see also discussions of whether "kink" (BDSM, etc.) is "queer" even when the participants are hetero (marginalized sexual minority, yes, but...). The actual, practical, oppression/discrimination/etc. against queer people doesn't map so well on to asexual/kinky/poly/etc. folks (though there is some overlap of issues -- obviously in wanting one's sexual identity to be understood and accepted by the mainstream but also not wanting it to be illegal -- this maps most clearly onto kink, though the marriage issue is also clearly relevant to some poly folk).