First of all size is a relative thing. It depends on what you mean by big. I would not write a monolithic code base with JavaScript. That's just silly, and is the kind of thing that Dahl and Schlueter have, themselves, been debunking in order to place node in the credible spot it deserves.

Second, you're citing company's that use node in the niche roles that work great for node. For example LinkedIn uses node for mobile rendering, they use Java for everything else (http://hurvitz.org/blog/2008/06/linkedin-architecture) and (http://engineering.linkedin.com/technology). I really doubt that if anybody saw LinkedIn's use of node relative to their use of everything else they would call it "large".

Now relative to most Python and Ruby projects out there...

Yeah - you can use node for large projects