We need to close tags in HTML they say but I don't see any reason to. Things like: </body> </html> make no sense at all. It's as-if the end of the document is unknown. Then how does the HTML inside the document continue after the end? Why should I say "ok here the HTML ends" and "now the document ends" ??? I cant imagine there is one browser unable to render a page missing the </html>. Some things should not go inside another like a table should not go inside a <p> but it's easy to assume the <p> is closed as the table starts and call it valid.
It's just like the quotation in links <a href="http://yahoo.com" >link</a> really is the same as <a href=http://yahoo.com >link</a> Putting 500 links on a page means 1000 times " to make it valid. Adding more quotes for ID's and classes, slashes before the > creates a lot of extra data but it's pretty much a heavy package of nonsense luggage.
It doesn't look like intelligent design at all. ROFL Look at WYSIWYG editors! The key component of content management systems. They empower non-technical users to manage rich content efficiently and intuitively. Unfortunately, WYSIWYG editors are notorious for generating "bad" markup (or "dirty code"). In the longer-term, the problems that bad markup creates can outweigh the benefits that WYSIWYGs offer.