The skills you list involve very simple knowledge acquisition. Once you have core CS competency, you can pick those things up very easily, and do a better job by far than the person that lacks the core CS competency.

To use your examples:

* I'd never worked with web CSS, but I built a CSS styling system for iOS, and used the CSS spec for inspiration.

* I've never worked with web analytics, but I ran a team that built a real-time (non-web) custom analytics/logging/querying system for a huge consumer-facing corporation.

* My team had never written any sizable JavaScript, HTML, or CSS, nor had any familiarity with prototype languages, but we were able to bang out a comprehensive HTML/JS XMPP client using BOSH in a couple weeks. We had an external HTML and web design expert on-hand to actually make it look pretty.

I think the real reason the engineers don't adapt is that we'd have to go work in environments that are filled with less skilled people using frustratingly knee-capped technologies. I might be able to stomach HTML/JS/CSS despite their myriad of flaws, but I'm not sure I could do it if I also had to use Rails and Ruby working for one of the existing players.