Come on, what kind of percentage are we talking about here? Tiny. Absolutely tiny.

Take ten minutes right now and read through the CoffeeScript reference-- poof, you learned it. It is just JavaScript.

Well, you haven't learned it unless you memorised absolutely every aspect of it, which you're unlikely to do on a first read. And it isn't "just" JavaScript- it has significant whitespace, different object notation, etc. etc.

Don't get me wrong, I've started using CoffeeScript and I like it. But it's a tiny, tiny minority language. There are a ton of JavaScripters out there that haven't learnt it because they don't need or want it. That's their choice.