Christ, that's some serious bubble effect you've got there. Not only is it possible, it's quite common. Until about 2 years ago the only place javascript ran was in the browser or a handful of experimental projects. And big, traditionally-organized teams often have people who are responsible only for the browser side of things.
Perhaps in silicon valley, but outside it most of us were expected to be a jack of all trades. There may be a specialized DBA, and a designer, but we were responsible for understanding the full stack. The designer worked in photoshop, and the DBA only came in on designing the tables and optimizations, but we were responsible for the real work.
A jack of all trades "might" work, but honestly it depends on the person. Someone who understands the full stack is usually not be someone qualified to be building scalable fault-tolerant pieces of server side infrastructure for a company.
Node.js is so easy to screw up, so difficult to debug, and little things can take down your entire application.
The combination of the language itself in addition to the type of people who typically would choose Node.js over other more proven options would make me worried that a blind choice is being made based on language alone and not proper evaluation or understanding of the other options available.
Personally I believe it is far better to be a language-agnostic company that thinks of different server side components as services, which might be in different languages instead of trying to use a tool just because they know the language already.
If anything I'd say you have it backwards; the kind of structure you describe (and the very phrase "full stack") is a very silicon valley/startup thing. It's larger, more traditional software shops that tend to slice the stack into separate vertical layers and give different people responsibility for each.
Of course there are many companies large and small that do it differently. But having someone whose responsibility includes client-side javascript but not server-side code is not by any means unusual outside the valley, at least IME.
Perhaps I am generalizing based on my experience in Tucson, which is close enough to cross-pollinate with the bay, but most places I worked and interviewed and had friends expected everyone on the team (apart from the DBAs) to be able to touch any part of the stack.
We also tended to have companies with small teams.
The only vaguely plausible rationale I could conceive of for your ridiculous assumption that all client-side javascript engineers would have server-side experience was an underlying assumption that any job in client-side javascript engineering would involve server-side responsibilities.
Evidently this wasn't your actual reason for thinking that, which just leaves me even more bewildered by your position.
