Making Iceman gay affects one title, X-MEN. There is no solo series for Iceman and there never has been, apart from a limited series.

For the Avengers that you’re talking about, such a revelation would affect multiple titles, and there are long running solo series, in some cases many of them–which also means the amount of evidence indicating the sexual orientation of the character in question is far greater, and more difficult to plausibly overturn.

With Iceman, fans have been speculating for decades, back to the days when I was simply a reader, that Bobby might be gay. So while it was never something that was on the page, it was something that was in the zeitgeist. The same can’t really be said about Captain America or Iron Man–there are some who might like those characters to be gay, but that’s a far cry from genuinely believing that they are gay, if you see the difference.