Guessing maybe it has to do with Xmillion people banging on the door for Heartfire? As of 1:30am Eastern US time, it was not up for d/l. I wanted to get it for my daughter (last day of summer vacation). But alas, XBL is not so lively.
I would have imagine dawnguard demand would be higher. But seriously, perfect timing by microsoft here. Think of how many hits xbox.com is getting. Pretty soon it'll be ranked higher than google.

Kinda serves us right, I guess this is how it feels to br a sony really devoted fan.