Well, ok. It doesn't really effect gameplay. But then, I'm not just looking at the statblock from just a gameplay perspective, either. If I need the straight stats on your run-of-the-mill Balor, then it's fine.
But I'm a guy that likes to tweak things. I'll adjust stats on a monster here, or build one up from scratch. Why obscure the rules? I don't get it. We're trying to teach people how to play, not confuse them even more.
I think HD type should be there, because it's an easy reference to "creature type determines HD type," so if I'm looking at a Balor, know it's an Outsider, and it has d8 HD, then I know that all outsiders have d8 HD. That's a useful reference to me, and given the size of the statblock right now, it does not take up significant space.