Man, you guys are sure giving me a hard time.
I am talking pure and complete beginners...the ones I normally work with. They start out not even knowing how a link is created. Most of them don't even know there is code which creates the page. It is easier to learn CSS later if you have the basic knowledge of how a page works with just HTML.
The learning curve is steep already in the beginning. They need to see at least a little success as soon as possible to maintain their motivational levels.
We focus on very niche areas with very small sites; this is the only chance a pure beginner has in seeing success in a few months with AdSense.
Choosing the right niche, knowing how to research the keywords and applying basic SEO principles, and optimizing plenty of original content are far more important factors in the beginning than whether they build those first sites with CSS or simple HTML.
In fact, a small site (in a very niche area) filled with great content which is optimized for the right keywords will rank just as well whether it used CSS or HTML.
I am not saying they won't or should not ever learn CSS, etc.