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.
That somebody can do both things should, in my opinion not mean that he has do both things.
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?
And that is how it's relevant. Any developer who can't grasp this concept has no place working for a company producing web-based software.