Eh, Link is always more popular than Mario on this fan stuff. Just look at the current VGC poll (Zelda > Mario). When Gordon beat Link last round, that was it. Poll was finished.
Freeman... yeah, not much to say about him, except I don't like him much. This poll is run by Steam (advertising) / PC users anyway, which explains the odd results. I'm not just saying this out of my love for Nintendo, either, it's odd enough he knocked out Snake (who surely has a larger fanbase). Since you don't even see Gordon in game (the character you're playing), he's never hyped up like the other characters. Of the Half-life fans I know, none of them are crazy about Gordon (the same can't be said about Snake, Kratos, Link, etc).
Anecdotal? Sure, but that's how I see it.