What is the rationale for the fact that
@someone used on a page is not being matched against any user which has taken part in a question (whether this the question itself, an answer or a comment)?
I would find it easier to be able to mention anywhere (on the question page) that
@janedoe said this and that but
@johndoe was more correct and having them being poked (since their name was mentioned) which could trigger a considerable improvement of their comment/answer/question (or a chaotic exchange).
Today this is usually a plain @someone in a sentence which does not do much, and particularly does not help to ether immediately identify the user, or warn him/her that there is something going on around what she/he wrote.
EDIT: @AdamDavis answer shows that I did not emphasize enough that my question was about "anywhere on the page") and not only comments, so I will improve it and he will never know because @AdamDavis was not recognized...