I think it's a hard leap to make to say that anywhere there's a "todo" or "fixme" in a comment means that it's the purpose of the comment. JSLint, for example, only warns when "TODO:" is at the beginning of the comment. 

We try to make rules as specific as possible to avoid confusion. I can see a case of saying that comments beginning with all caps is very specific and easily identifiable. As soon as you start talking about any capitalization in any part of a comment, that starts to feel too broad as a general rule.