This is a beta, after all: the primary function is to see how the game handles things when a massive wave of players start playing. Second, it spaces out the server load for developers that are still seeing how a game will handle a large influx of players. This serves a few functions: first, it rewards players who purchased early and gives them a bit of a reason to feel special. Players who pre-ordered the game get early access by two days before everyone else gets to check it out, usually over a weekend. Betas have become pretty par for the course for most AAA games with some sort of online component, and this is usually the schedule that they follow.
