Here's Walt Mossberg writing for the Wall Street Journal:

Microsoft also offers a program that, for $99, will turn users' Windows 7 PCs into Signature versions, if the owner brings the computer into one of its 16 stores, due to grow to 21 outlets in coming months. All Signature computers come with 90 days of free phone support, as well as help at the stores' "Answer Desks," which are like the Genius Bars at Apple stores.

Yeah, that's convenient. People purchasing Windows computers are the same people who won't spend $0.99 for an Android app.