I don't think so and I don't think that's the reason behind this move.
I'm pretty sure this is about gaining back some developers. All the cool things happening these days on mobiles and on the web are not happening with Microsoft's platforms.
It's important to remember from where .NET comes from. It was part of a larger vision of Microsoft that included Windows Longhorn, .NET Passport, project Greenwich and Trusted Computed. Of course this vision screamed "Lock-In" and it was about just that (too bad that it is happening anyway, yet people aren't paying attention anymore). So .NET wasn't opened because it was seen as a way to keep people on Windows. Sure there was an ECMA standard, but that was just like putting lipstick on a pig (though ironically that ECMA standard is much stronger and useful than Java's JCP, which is a complete farce).
Unfortunately they missed the forest from the trees. The web developed outside of their walls, mobiles developed outside of their walls. All the cool things happening right now are happening outside of their walls. And now all of a sudden, a Windows-specific platform becomes a liability, a way to keep people out of Windows or whatever Microsoft wants to do.
Personally I'm happy about it. It's a pretty solid platform and a good alternative to the JVM. Given the dickish moves by Sun against Apache Harmony and by Oracle against Android's Dalvik, I think it's about time the JVM had some competition. .NET is still missing a healthy ecosystem though. For Java / the JVM the ecosystem is intimidating at first (e.g. so many choices, so much open-source, multiple IDEs, multiple languages, WTF), but it's actually its biggest strength. On the other hand if there's enough interest, then .NET can catch up as the basics are taken care of.