I am certified in Tech Apps, and I have can also teach web mastering as I taught it before you have to be individually certified in it. In other words, I've taught a lot of web mastering. I really hate doing it though.
First, I'm not an artist. Yes, I can look at a website and know it sucks. I can even design some elementary graphical art if I can find a tutorial that does what I want it to do.
Second, I'm a programmer. HTML coding is not programming. It's doing what I am doing now, typing. It's got a simple set of rules but so does desktop publishing, etc. Code is at a much higher level and is much more fun. HTML coding is boring.
Third is projects. High school students are horrible at long terms, as a rule. There are exceptions, but the kids that are attracted to a web mastering course do not have the attention span for a long term project. In fact, CS kids do better if they can finish an assignment in a class period, and thankfully most of the projects in my CS courses are one day projects.
I really admire the people who can teach web mastering and multi-media, BUT give me a math class any day over the tech apps courses.