I don't necessarily think that's a fair question. If I were to start a big-name consumer app today for Windows, I'd choose C#. But most of those types of apps

I don't necessarily think that's a fair question. If I were to start a big-name consumer app today for Windows, I'd choose C#. But most of those types of apps have a long history that either predates .Net or predates .Net being all that great. Because of this, even a lot of Microsoft's apps are still written in C++. I'm pretty sure that Microsoft would completely rewrite say Office in .Net if it could do so without losing decades' worth of code.