Gaining reputation takes time. It takes a steady stream of useful contributions. The purpose of the reputation cap is to keep individuals from receiving an undue number of abilities for one crazy-popular post. You don't want users coming out of the private beta with a bunch of abilities they might not have received otherwise. The private beta is a type of "dress rehearsal" before we open this site to the public. As such, you want the activities and behaviors to be as much as possible like the actual site.
In a bigger picture sense, reputation (as a metaphor) is the currency that drives the economy of this site. And for that currency to have value, it has to be a limited resource. You can imagine, for example, that someone who REALLY wants this site to succeed would simply go around up-voting the top users simply to get people up there. That sounds like a good strategy on the surface, but how would folks know if their their content is being well accepted (and correct) if the up-vote means nothing?
Up-votes and reputation are a limited resource, so you have to pick and choose the best of the content you feel is deserving — and that is by design.