Due to "InfinityEdge Display", there's no room to put it anywhere else. It does make the built in webcam rather useless, I've got an external (Logitech 920) webcam.
They should have done something like this, but it's Dell, not Apple.
I've used a number of their top of the line products over the years, and they've always been riddled with cost-saving compromises like this. If they put the bezel on top, they'd have to invest more money into the display hinge as well instead of whatever cheap plastic parts they currently use. That would eat into their profits, so it won't happen until the competition forces it.
