Masiah, there is no point in having a long beta. The beta is purly there to make sure any major problems are delt with and ballence is approximatly correct. As the game is working prety well for the target group, they want to have it out as soon as possible.
Remember that there are going to be 2 expansions. They will have to opotunity to do any additions to the engine with them that the beta is currently lacking. Additionally just cause the game is released does not mean it wont be patched. I expect quite a number of patches by the end of the year.
An example of what betas are for could be seen with the new Halo game. The beta pointed out major service issues with the game to the developers so they could fix them (thus there will be no service issues on relese).