As I already suggested here, it would be nice if the OP is also notified of comments on answers when @OP's-user-name is used, even if the OP isn't a participator in a comment discussion on that answer, yet.
This way, I can e.g. make an (IMHO) important comment on an answer and notify the OP.
I think this is worthwhile. Today on English.SE, I asked a question, got some answers, and someone tried to ping me on an answer. I only noticed it because I actually came back to look at it again.
If it's that important and the OP hasn't participated in that answer yet and you think the OP won't notice it when reading answers later (but if he doesn't care that much...), then you should comment on the answer and the question. Delete one of those comments later. All three of these conditions combined should be really rare.
I only want to check one place to see who will match, especially on questions with several answers (say 7-9). Not the current question and somewhere else, even if that is only the OP's name. You'd have to determine a sort order, and it's just not worth the complication. Keep it simple. If you must ping them, you know how to do it: comment on the question.
Stack Exchange isn't instant messaging, even if it's important we can reply sometimes.
Being able to @<asker> (and "ping" the question asker) in comments to answers where the asker has not yet participated is generally expected behaviour. There is nothing to suggest (at the time of posting) that this does not have the desired effect. As @Catija has stated:
a relatively common point of confusion about our reply system.
In my experience, "relatively common" is an understatement. I see many instances of this "expected" behaviour in the wild. I myself thought it worked this way for years(!) before finding out only recently that this does not have the desired result (consequently many many comments I've posted have quite possibly been in vain).
Typical/common use cases where this is "necessary":
You need to notify the asker of an important update to your own answer. This might be after the answer has already been accepted (when the user is less likely to naturally revisit the question).
You need to notify the asker because of inaccuracies in an accepted answer.
Having to "ping" the asker by commenting on the question itself is very counter intuitive. It is also "messy" and promotes out-of-context comments on the question. (Comments on the question are intended to seek clarification about the question.)
