NOTE: Those buttons are not site wide, they stipulate that the page which has them validates, so if a page does not you don't use them on that page, as it is a template they are automatically included even if you break validation in your content for instance.

I would argue the "Best Practice" comment, I know of few who consider it best practice. It only strokes the owner/designer's ego. It is meaningless to normal folks and to designers... we would expect it to validate with or without. They are useless on templates because pages show them rather they validate or not... and odds are if you use for instance a Flash header in the template, no pages will validate. Then you can break validation in your content easily to invalidate a single page... or in the case of Blogs etc., odds are hight that the user will invalidate your pages through their comments. So at any one time you may have many pages not validate and not know it. Bit embarrassing to claim validation when it in fact does not. So most designers I have discussed this with find them useless and/or misleading and therefore not best practice.