[nene]

I would argue the contrary, that the very reason why HTML took off so fast was that any fool was able to craft a site, and it would work even if it had a few bugs in it. Failure tolerance is a great feature. Especially if you consider it in the context of document authoring - for which HTML was originally designed for - it's better to read a document that has one unclosed <b> tag in it, than to be completely unable to read it because there's a syntax error in markup.