The reason is that C# had a chance to learn from the experience of others and is still a relatively new language.
There is a little bit of cruft here and there. For example, ,NET had good threading support from the start, but the idioms that are used nowadays for concurrent and parallel programming have evolved, and while the old APIs are still there, developers now use APIs that are more up to date.
Is it just me, or it is a bit hypocritical for Mozilla to be talking about the wonders of the Open Web and then embracing two very proprietary developer platforms to promote Asm.js
If they cared about the open web, and they cared about open source, they would be helping open source game engines like Ogre3D and Torque3D.
Instead, for the sake of expedience, we see them promoting proprietary components.
It was not too long ago that they were lecturing the world on the evils of proprietary video and audio.
We love F# and it continues to be both an inspiration to other languages at Microsoft, as well as API developers.