I wonder how many people think it was unreasonable due to how you had to send back the page to be truly valid; application/xhtml+xml, application/xml, or text/xml. Due to IIS, browser support, and the platforms I personally used, that was the only requirement I never felt I had to meet.

I personally agree with you, and still close my tags, use quotes around attribute values, and provide empty/duplicate values when needed.

I also still use XML for data storage, and used ColdFusion back in the 6/7 days, so that probably had a influence on my choices.