I am guessing the cooling needs access to those vents and Microsoft didn't want to lose a bunch of money on customer service calls/warranty claims from people blocking them.
Yeah, the black version is much more beautiful (to me). And I would've loved if the disc drive wasn't attached to the side like a tumor but rather placed in the middle, like sane people would do. And it should be smaller. Those are my main 3 complaints. But then again, people are talking about the design... so maybe it's a success?