According to posts on the MSDN forums (e.g. http://social.msdn.microsoft.com/Forums/en/netfxsetup/thread/347bc59c-374c-43f9-a2ed-e9bb89c6f25b ), Windows 7 includes the .NET Framework 3.5.1.
However, this is an optional installation (perhaps it can be disabled more correctly):
On Windows 7, it includes the .NET Framework 3.5.1 as an OS component. This means that you have installed the .NET Framework 2.0 Service Pack 2 (SP2), version 3.0 Service Pack 2 (SP2) and 3.5 Service Pack 1 (SP1) plus several bug fixes after updating 3.5 SP1 if you installed Windows 7 Thus, you do not need to manually install .NET 3.5 SP1. We can add or remove the 3.5 function from SP1 using the Control Panel Programs and Features.
Microsoft really should have official documentation that makes it clear somewhere, but this is the best I could dig.
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