I'm afraid you're missing it a bit - just making only javascript applications is the reason to make a different distinction - some people are better at doing MVC, and they do it in the browser now; while some people are great in making great looking UIs, but not really digging into application architecture. And, of course, there are people doing both, being full-stack devs, but still they're usually more efficient in some areas than the others - I am such an example, still I know UI devs that are way more efficient and know neat tricks on the UI, as well as some great UI libraries to do their work faster (and usually better, relying on the know-how built into the lib) because they specialize in that.

Thanks for your comment regarding labeling, though... I agree that sometimes it's inappropriate, still sometimes it's useful to figure out the kind of work being done under such a label