[thomasptacek]

Not really. First, they have very little to gain from keeping .NET closed: there are strong open-source replacement projects for the "proprietary" framework classes, and .NET assemblies don't really protect source code, even when obfuscated.

Second, even if that weren't true, opening things up is actually not out of character for MSFT, despite the conventional wisdom. For instance, you can download near-complete debug symbols for the underlying operating system. If you've ever read assembly with and without PDB files in IDA Pro, you know what a big deal that is.