And how is that relevant? I've heard the argument "Your backend developers can work on the front end too" -- but its a tired argument. Any developer who can't already do both has no place working for a company producing web-based software.
There's a huge army of teams who aren't competent to do both, judging by the number of sites that fail completely if the client isn't trusting and running javascript. Node.js seems like a good solution for unobtrusive enhancement, making reliable semantic resources that may still optimize out many server round trips with mobile code.
In a perfect world you would be correct. But answer me this:
How many Java backend engineers know how to unit test javascript, how to make modular templates (e.g. writing their own tags, or nesting/tiling their JSP's), how to systematically minify their code in production and use CDN's ... or even how to use any design patterns in Javascript?
I think everyone here will back you up on that, but don't infer that zinxq is advocating choice by technical dogma. I read their post as simply asking for an explanation for node.js's accelerating popularity; of course there are many factors, but its ability to reduce lexical context switching is obviously a major component. To argue otherwise would be ill-advised.