The hope is that newer sites (and sites using WineVine DRM are newer, relatively speaking) aren't written as poorly as old ones. Well written sites use feature detection, not user-agent detection. This move by Microsoft addresses problems with older sites, and IE12 supports these older features that the site doesn't belive IE can support.
Building a website that has to work on Internet Explorer is like teaching.
Its like having to teach the class to the dumbest kid in the room. You can't take the dumb kid outside for extra instruction (because that would be browser targeting.. ).
Everyone has to wait, until the dumb kid gets it.