@Humulus_lupulus most fellowships give you until May 1 or thereabouts to commit-- so it's not really a problem so long as the ones you'd seriously consider release decisions in April. I have NSF, for instance, but I'm waiting to commit until NDSEG is released in case I get both (questionable, depending on whether NDSEG accepted a late rec) and NDSEG has some awesome package (they used to have a higher stipend, but that might not be the case anymore).
This is also why NPSC (there's only like, 1 serious thread on it in the bank), on the other hand, is sort of a mystery to folks. In the past they've released some acceptances as late as mid-May. At that point, yes, some folks have probably already committed to other fellowships. I was an alternate selectee for NDSEG last year, and didn't finally hear back that I didn't get it until May 10. If I'd had NSF last year, that would have been too late (though you can theoretically do both and defer NSF).
ANYWAYS. Lots of words to say that they have time, and the main reason earlier would be more helpful is that grad students already have enough on their brains. haha