This one actually has a simple explanation. If you @someone when they are not already involved in the question, they will never get notified. Your comment is therefore simple noise.
More generally, Stack Overflow is not a communications platform, like Twitter or Facebook, and we'd like to keep it that way.
If you really need to notify someone about something (you really don't, but...), then the comment goes on one of the person's posts, so that it can show up in their inbox. The only time I've ever done this (other than as a part of my moderator duties) is when a question was posted about some person's software project, like Leppie's IronScheme, and I thought they might have a personal interest in seeing it.
This is still not necessary if questions are tagged properly; I would imagine that Leppie monitors the IronScheme tag anyway.
As to the feedback part, think of comments as temporary post-it notes. Comments are second-class citizens; their only sanctioned purpose is to clarify a post, or ask for clarification. Any other use subjects them to removal without notice.