I should have done a better job of clarifying that I was referring to the majority of business developers rather than the 1% of devs talented enough (and so inclined) to work on compilers and frameworks.

However, I would definitely not restrict my characterizations just to web developers. I spend most of my time in the application logic layer (libraries exposed as dlls). It has no UI but still relies heavily on extensive libraries (.NET BCL) that handle all the low level plumbing. The business logic I write can be complex at times (in a state machine way), but it is hardly ever low level in the way that traditional algorithms are.

To write those frameworks you would need to know about algorithms. To write the compiler for C# you will need to know about semantics and compiler theory and logic and functional programming and many more subjects which are traditionally tought in a computer science degree.