Read the article, there's no way to specify "optional closing tag depending on whether a `src` property is present" so therefore it's manditory. You can, of course, write the parser to do it, but there isn't a way to express it in the HTML grammar.
I always have wished that the script inside the tag would be executed if the `src` couldn't be loaded, which is something John Resig suggested years ago [1].
[1] http://ejohn.org/blog/degrading-script-tags/
