A quick example: look at document.cookie. They are referring to DOM2 information. It's undergone some (slight) changes in HTML5. Nothing is referenced, even though that section is relatively stable and marked as safe for implementation. That's a 2000 spec vs a 201x spec. Nobody's even gone in and pointed out that this has changed in HTML5.
For example, I had no idea document.cookie got changed in HTML5, and I bet neither did anyone else involved.