Because going DP-only significantly reduces complexity and cost, and results in a thinner screen. This is probably the 3rd time I'm posting this, but oh well: http://displayport.org/simpler-setup/Direct-Drive.htm
Screw HDMI. The connector sucks and the licensing sucks. Too bad HDMI will be around for a while yet.
Oh, and the Apple Store is back to saying "Ships: November". WTF Apple? Get it sorted. WANT.
YOu're in an awful big hurry to get a "Rev A" Apple product. Haven't learned the hard way yet, I'm guessing?