This is actually a smart move by Apple. I like it.
Most of the general public doesn't care about trials and beta versions of apps. The Mac App store will be a success simply because it will provide a simple, easy way for most of the general public to get applications for their Mac. For the few people that care about trial versions and betas, they can still get them the same way they always have. No reason to clutter up the App Store with multiple version of the same software. Clean, simple and reliable. This is a good thing, folks.
Agreed, I am actually glad there will not be any beta style apps....