What I don't understand is that it's not difficult to validate. Sure, if you buy a template and W3 tells you you've got 200 errors you're pretty much screwed, but W3 tells you what the problem is, and after fixing a few sites with validation issues you're bound to remember what not to do.

One problem could stem from not understanding what doc types accept what. So with that in mind I can understand why some seasoned designers have some trouble with past habits, and n00bs do just fine. But honestly, everyone in IT knows you've got to keep up to date with continued training.