There is definitely value in HTML/CSS skill set. The question though becomes, are there enough jobs available where only those two skills are enough of a value to get a well paid job. I think the way the market is, you have to add to that skill some related skill set to the table, such as Design, User Experience Architecture, User Testing expertise, etc.
I strongly agree though that there is a healthy limit to what a single person can truly become a master in. We shouldn’t fool ourselves to thinking a “full stack” developer has actually mastered every piece of a technology stack. I think the T-shaped developer description is a much more accurate (and healthy) description of what a workforce should follow and strive for.