On the other hand, vanilla PHP effectively "hides" HTTP from the programmer. I taught myself PHP in middle school and high school as my first programming experience, and had no concept of a thing called "HTTP" for a very very long time. I knew the pieces of it that PHP gave me. I knew what $_POST, $_GET, $_SERVER, $_HEADER, set/getcookie(), were and how to manipulate them, and I knew the rules (setting a header after "echo" made it complain), but I didn't understand how that all hung together as a thing outside PHP called HTTP.

When I did learn about HTTP, it was very easy, since I already knew it without knowing I knew it, so maybe that's in favor of your point, but there's much to be said for the actual understanding that I didn't have at first. When I started interviewing people for PHP entry-level jobs, asking about HTTP was one of the ways I gauged how well applicants understood their work at a conceptual level.