In places outside Twitter, the @foo idiom addresses a comment to that user, but that's not always what I intend when I reference a user. I'm simply trying to prevent evaluation of a token as English text.
I understand where you are coming from, but I think that at this point the interpretation of @foo as an idiom for not addressing but merely mentioning a user has permeated most online cultures.
Those who really do not know (yet) will quickly understand from context.
All in all, I think @foo is less confusing than 'foo, and will spare you questions like in this thread.
I think the @user idiom is by now understood by anyone not relying exclusively on pigeons to send their missives.