I was wondering lately why are web sties still adding the (X)HTML/CSS-valid buttons? These seem to be the equivalent of the PC stickers for the web pages - something that had its role back in the days, but is now nothing more than just a visual noise.
Yes, validating your website for (X)HTML and CSS standards compliance is important, there's no arguing about that. It ensures your users will get the most consistent experience in various browsers. However, the validation results are actionable only for you, as the owner of the website; there's nothing your users can (or should) do if that validation fails.
Besides, most of the people out on the web care not about how well your site validates. They care what their experience is and how relevant is the content you publish for them. Yes, a non-validating (X)HTML may affect their experience; however, even a site that adheres to the newest HTML5 drafts out there may still offer a horrific experience.
Here's my call for action to all webmasters: As one of your users, I implore of you - get rid of the webpage stickers.