FWIW, that same creator created Jade and Stylus which are pythonic like CoffeeScript. What's wrong with HTML and CSS? I could never take his stance against CoffeeScript seriously.
I can't speak for him. I've had fellow programmers love CoffeeScript for their own personal / client projects - but they conceded that for the real deal - a public open source project should stay in JS. Otherwise, it'd scare off swaths of top tier JS coders from contributing. Atom serves as an example of this practice [1].
The smell CoffeeScript in core gives off to them - while I don't subscribe to this - is that "it's an amateur job, don't bother". You don't write open, core code in an abstracted language. That's so suspect. Personal / internal projects are OK, a few I save CS specifically for those situations.
If you look at the source of Express.js, you can see the javascript has it's own aesthetics to it. You can think of express/connect as serving exemplary of node.js code, for now.
On a topic of the CoffeeScript creator, Jeremy Ashkenas also created Backbone and Underscore. These are pretty much examples of top tier JS in the browser. The projects are known for their annotated source:
You can't output this kind of code with CoffeeScript. You have to let in sink in and understand the patterns (the way .extend works in underscore and how Backbone builds upon the idea to add it to objects.)
