Gender as the core of the marriage debate?

From the National Transgender Advocacy Coalition:

"The good news from a Florida Appeals Court July 23rd decision is that Michael Kantaras retains custody of his children, at least for now. The bad news is that his marriage has been declared null and void because “the trial court erred by declaring that Michael is male for the purpose of the [Florida] marriage statutes. … The question of "whether [a] postoperative transsexual is authorized to marry a member of their birth sex is a matter for the Florida legislature and not the Florida courts to decide."

Also, this morning I went to a training by a staff member at the LA Gay and Lesbian Center about campaigning for marriage equality, in which someone asked whether gay marriage would "apply" to transgender people. The question revealed (1) the inadequacy of the phrasing "gay marriage," (2) the way in which the marriage debate turns fundamentally on notions of sex difference, and (3) the unpreparedness of the trainer, who confessed, with a knowing laugh, that the transgender "aspect" of this issue was the part he found the most confusing, and that it would have to be addressed on a state-by-state basis [which neither answered the question nor differentiated this "aspect" from other marital matters].