Usability, XHTML, and DOCTYPE

I'd have to agree with everyone else that the article about website usability was definitely the most interesting this week. Actually, it reminded me a lot of what I have learned in journalism about what readers actually pay attention to and where to focus attention to as a writer, photographer, or designer. In a newspaper, there is something called "above the fold," which is basically what readers will see when they pick up a newspaper off of a news stand before they open it. If something does not catch their attention on the top-half of the first page, then they will not buy the paper. I think that the same applies to a webpage and what they call "above the scroll". Also, white space is sort of a refresher for a reader - or browser. No one wants to read a huge block of text (like what this paragraph is starting to become).

As far as reading about XHTML and DOCTYPE, it was a lot like reading any other programming writing. I find that articles or books like these are more for reference than enjoyment (you wouldn't read a dictionary for fun, would you?) I understand the point of DOCTYPE, however - and how it preserves the look of fonts. I would like to know why someone would use XHTML instead of just HTML, though.