I don't think tha gmail90 was referring to validation. Validating really doesn't have anything to do with having a clean, nice code. You can have ugly code and validate. And with clean, nice code, I don't mean that everything appears to be in the same line.
I think we're talking about the best practices that we're supposed to follow for accessibility purposes... but in true most people follow because it would boost their ranking in Google. These suggestions are, indeed, suggested by Google itself in their blogs. Yet they don't follow them.