Originally posted by Zach Elfers
Oh. I thought that the <html> tags were required.
Yes, it's a very common missconception.
The HTML/HEAD/BODY ENTITY is required, but the TAGS (which mark where the entity in question start and end) are optional.
This leaves it up to the webbrowser errorcorrection to figure out where they should be (and thus leaving them out requires more CPU from the visitors comp to render the page).
Most designers thus add these tags, both for their own sanity as well as the reciving computers.