Plenty of things do. Such as web analytics tools & plugins that can only work in a non-xhtml-compliant way.
My favourite was a google tool (can't remember what it was - google website optimizer?) that required you to use some godawful <script> construction that was necessarily broken. And you'd have thought google would know better.
My favourite was a google tool (can't remember what it was - google website optimizer?) that required you to use some godawful <script> construction that was necessarily broken. And you'd have thought google would know better.