How many one man dev shops (which is what we're talking about here) test well, or even in in multiple browsers? So yes, if you get a web site from a one man web design shop, then you should make sure it validates.
If it doesn't, it's probably rendering in quirks mode, and you'll have all sorts of problems with the layout if you need to change it.
If it doesn't, it's probably rendering in quirks mode, and you'll have all sorts of problems with the layout if you need to change it.