I got the impression that by pre-ordering you get those unlocked by default but you can still unlock them the normal way, but maybe I'm wrong.
I'll be annoyed if that's the only way to get the grenade belt. I mean, I plan on preordering from gamestop anyway, but that sort of thing irritates me.

e: wait, I was annoyed if the bonus you get for preordering is unlockable anyway, and I was annoyed if they were going to give a bonus for preordering that nobody else would be able to get. I'm literally impossible to please in this instance! Maybe they just shouldn't be giving this sort of bonus. :P