Help get this topic noticed by sharing it on Twitter, Facebook, or email.
You can still continue using the 2nd edition examples. They are all valid XHTML, which is a respectable standard used on a large number of professional websites.
The 3rd edition examples use HTML5, which is successor to XHTML 1.x. The main difference is the doctype and a few of the rules about syntax. Notice that I don't say the examples use HTML5 *features*, because they don't, as most of these features are not yet supported on the majority of browsers. In fact, the HTML5 examples look pretty much the same as they did when they were XHTML examples, only there's no need to worry about "transitional" doctypes.
If you want, you can download the HTML5 examples from the 3rd edition, to compare the difference.