The point is that in web frameworks, the two are often confused or at least blurry. So we need to extend the essential/accidental dichotomy to deal with global versus local views.
Take for example parsing emails. In a universal sense the complexity is accidental, it arose from the technology decisions of the authors of RFC822 (which partly arose from previous decisions).
But locally, for a web programmer, the email address format is an immutable, irreducible fact of reality. I can no more wish away that complexity than I can wish myself a million dollars. To me it is an essential complexity.
Where web frameworks of the entirely-made-out-of-code variety really shine is in facing up to these locally essential complexities. It may seem superfluous now. It may not seem so in six months.
What programmers like B often doesn't realize is that they push core logic of the application from their source code (Turing complete, expressive, versioned, benefiting from static and dynamic analysis and all the testing/refactoring tools available for the language) into an obscure XML notation or even some proprietary rules database, worked upon by a complicated blob of 3d party code that has nothing to do with the original business problem.