http://blogs.msdn.com/b/mshneer/archive/2010/03/10/design-of-vsto-2010-runtime.aspxWhen migrating VSTO solutions targeting .NET 3.5 to .NET 4.0 people are noticing some design changes. Our documentation on migration puts it pretty straightforward about this and does not explain the underlying reasoning for these changes: "If theen-USTelligent Evolution Platform Developer Build (Build: 5.6.50428.7875)