I agree with you. HTML is markup. It is scripting. Programming involves:
1. coding
2. compiling
3. running
4. testing
5. debugging
Now C# with emebedded HTML is different ;-)
The difficulty level of Maths in your apps can vary from the very basic to the very complex.
What sort of apps have you worked on?
My opinion is, first HTML is not a programming language, is a MARKUP, TECHNOLOGY what ever you want it to call it, but not a programming language.
About math, i would say that all depends on what you are programming, but indeed you can do a lot of work with just the basic math functions.