Windows does have a C# compiler by default. It is located in the `Windows\Microsoft.NET` folder. Not very discoverable, though.
And starting with Windows 10 a metro app called 'Code Writer' seems to be installed by default for coding. (At least it's there in my installation.) I didn't try it though.
I'm glad. MS has made a lot of good programming tools. I really like Visual Studio and was a huge fan of QuickBasic 4.5 back in the day. Turbo Pascal was the killer app that first enticed me to the PC world.
It still befuddles me why some of this basic functionality cannot be a standard part of Windows. Not every Mac user uses emacs, or even knows how to open the Terminal app, but the fact that basic tools are supported means that there is just a baseline level of infrastructure to work with.
And starting with Windows 10 a metro app called 'Code Writer' seems to be installed by default for coding. (At least it's there in my installation.) I didn't try it though.