Seems like you're annoyed not because of anything about the song, but rather where it comes from. I linked three songs, all of them from anime. But they're all pretty much instrumental, and without looking them up you wouldn't have known they came from anime. Deadgye linked Rain by Steve Conte, an American artist singing an American song. But because he heard about it through an anime which you know of, it therefore pisses you off.
One could also argue that had those who link those songs not heard them in the context of anime, they might not have thought they were that great to begin with (and certainly would not have linked them as "epic music"). If you think a piece of music is epic because of the piece of music, that's one thing. But what I think he's getting at is that if you think a piece of music is epic because it appeared in a film genre that you are a huge fan of, your opinion might not be as valid to anyone who is *not* a fan of the same genre.
Honestly, I listened to several of the linked music from anime sources and found none of them particularly noteworthy, much less epic. I suspect that people associate emotions and images in their minds to music based on what context they first heard it. I'll freely admit, for example, that people who are not fans of Firefly likely will not have anywhere near the same opinion of the Ballad of Serenity as I do. And if I were to link to "epic music" that would not be a piece I would link. Because I'm aware that most people will find it "meh".
If you want to complain about something, complain about people basically linking the entire Bebop soundtrack.
That's kinda included within his complaint though, so win/win, right?