Given that VS2010 is the first version for a while that has a new runtime, I suspect that the required registry key has changed.
Otherwise assemblies listed for VS2008 (and it's 2.0 runtime) would be incorrectly listed for VS2010.
So, to make it work, you'll need to find the new key.
Update: I think that the information you need is here: http://msdn.microsoft.com/en-us/library/wkze6zky.aspx
Specifically, the path is now
[HKEY_CURRENT_USER\SOFTWARE\Microsoft\.NETFramework\VersionMinimum\AssemblyFoldersEx\MyAssemblies]@="AssemblyLocation"
where
- VersionMinimum is the lowest .NET Framework version that applies. If VersionMinimum is v3.0, folders specified in AssemblyFoldersEx apply to projects that target .NET Framework 3.0 and later.
- AssemblyLocation is the directory of the assemblies that you want to appear in the Add Reference dialog box, for example, C:\MyAssemblies.