I would like to start this request with a citation of the msdn blog entry regarding the new features of VS 2010 located here: http://blogs.msdn.com/b/terryclancy/archive/2009/05/19/visual-studio-2010-new-features-extensibility-points-and-partner-opportunities.aspx
There it says: "Second, we sought to decouple Visual Studio 2010 from its target frameworks so that Microsoft can ship new frameworks, framework profiles, and framework service packs without patching Visual Studio."
In essence there you say that, by the "Visual Studio Multi Targeting" feature, you would be able to support new versions of the framwork without changing VS itself. So there is no technical reason to not provide a targeting pack for 4.5 for VS 2010 right?
Secondly. The 4.5 framework is an in-place update of the 4.0 version. Even though you changed some parts of the CLR, it is still based on the CLR 4 (even the revision number of the clr did not change). Basically we could compare the 4.5 release to the 3.5 release. So lets compare VS 2008 to VS 2010. When VS 2008 was released it came together with Framework Version 3.0. Later on, with SP 1 the framework 3.5 was released. Both were still targeting the same CLR version so VS 2008 now supported 3.5 as well.
I think my point is clear. Why is VS 2010 treaded so much different than VS 2008? (Of course the answer is clear as well. Marketing.) I can only beg you ( or the product managers ) to please realize that it is not the right way to force the new VS 2012 version into the marked by cutting of new features from the former 2010 version. No offense!