why silverlight libs are in runtime v2.0.50727?

Why is the Silverlight libs built on the .NET runtime version v2.0.50727?开发者_开发百科 Is there any rational for not having the Silverlight libs in the latest available .net runtime? Or is it just a completely seperate product, and not possible to use any v4 .net libs within a Silverlight project?

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All silverlight libraries carry the same runtime version number. For Silverlight this version number is meaningless. Most SL libraries have the version 2.0.5.0 even those that were introduced in SL3. Some dlls that were introduced at or after SL 4 have 4.0.5.0 as their version.

In reality the version numbers have much less impact in the Silverlight world. This is no GAC to pull versions of dlls from. There is little in the way of hunting for dlls when a demand to load a dll is encountered, all the dlls referenced in the deployment are loaded on app start and referenced absolutely. Its not possible to load more than one version of a dll into the running instances of Silverlight either.