Authentication is already a fact of life on M$ OSs - Win9x was the last version to uncritically accept non-M$ approved drivers. WinME will still accept them, but moans and groans and
AFAIK XP won't accept them at all. It is a small step to extend this to applications.
There is some logic in this. Badly written drivers are a major cause of instabilities in Windows, so M$ instituted a driver certification program in which people writing drivers could submit them to M$ for certification and if it is found to be OK a Verisign digital signature file is given and installs into the %windir%\CATROOT folder. Don't know how much M$ charges for it's blessing but you can bet it ain't cheap...
Read details at
http://www.eu.microsoft.com/hwdev/driver/digitsign.asp
Given that misbehaving apps. can also crash Windows without difficulty it is hardly surprising that M$ is seeking to extend this to executables as well. Again there are some benefits to this (stability and [?] security)as well as a considerable downside. The downside is of course that eventually only M$ approved programs will run on M$ OSs this allowing M$ to completely lock up the market. Developers will HAVE to submit apps. to M$ for approval, otherwise they just won't run at all. M$ is is unlikely to give it's blessing for free and indeed may, in exchange, impose restrictions on the developer (such as assigning all or part of the rights to M$) so as to control ports of the app. to other platforms like Linux.
While deploring it, you have to admire M$ iron determination to lockup and control the PC world and the Internet utterly and completely and the myriad different ways that it is quietly going about it. What vision! What strategy! What chutzpah! And nobody, even the US Government and Courts can do anything about it...