I will read that tonight. Thanks for the link! I've been looking and looking, thinking that there simply had to be something else--something that challenges or at least questions the pattern. But I'd wondered if perhaps it was a pattern too embedded in commonly held prejudice to be noticed.

And yes, I had wondered whether the addiction issues figured in, and on what timeline. It's odd but I guess I just wasn't tuned into the fandom at the time enough to read boards or hear the crit (which is probably good, as I would've been tearing off people's heads left and right).

Just in terms of Angel vs. Xander, while it seems reasonable that Xander should change (because, y'know, human), the vampire thing suggests an unchanging body (which can make any change seem all the weirder), though of course anyone looking at Spike over the course of Buffy and Angel has to notice that Spike changed as well.

In terms of rationalizing or explaining it, I'd be happy to see someone arguing that somehow, vampires' bodies change in relation to blood supply (though much hand-waving has to be done there).

But for the humans (and I haven't yet read that story you linked to) my first impulse is to say that I'd rather it not become a h/c issue, because that's making too much of it--pathologizing it rather than accepting the mutability of the human body as a part of human life.