Falcon Northwest's points about it being available for the life of the series and having the SFF friendly cooling makes a lot of sense, and easily justifies the $100 increase, for them.
However, isn't MSRP +$100 usually the range which you'd expect to see binned chips in addition to the power...
Earlier they explicitly said that they weren't announcing a new version of Windows, so I would expect it to be an update like 8.1-2, 8.2 or something....
Microsoft showed windows 8.1 with a real start menu at Build 2014.
You can see it here:
http://channel9.msdn.com/?wt.mc_id=build_hp at around 3:10:00
They also mention being able to run modern ui apps on the desktop, instead of them just being kinda dumb.