You've probably worked out by now that HTML is a bit of a slippery beast, what with deprecated tags, and browsers that behave in odd ways. Like most software, it's constantly adapting and changing. W3C is trying to keep a lid on it, and encourage the right kind of development. HTML 5 is under development - latest editor's draft just out.
http://www.alistapart.com/ has great articles, I do recommend you check it out, including this one, which discusses some of the features of the new version.
