I think everyone writing content for the web should learn HTML and maybe some CSS - although the design part should be done by someone good with CSS, so that you only need to use semantic HTML, or you will end up with div's all over.
I think CSS is an order of magnitude more complicated than html, so I'd leave that to the professionals. But pretty much everyone should learn html, I agree with that.
With a little bit of CSS I mean enough to know how to add some extra padding to all buttons on the site, like finding button { padding 4px } and change that to 6px.
