There are two reasons to include the comment address inside of the required character length.
The first part is, is that the address is part of the comment. For extremely short comments, it may not be all that important, but in beefier or substantial comments, who is being addressed is actually an important facet of the comment. So it would deserve to count.
The second part is, it would be an unexpected result otherwise. We collapse whitespace so that is clear, but with the address, the characters are still there. This is particularly confounding if the address is just the 3 character minimum.
The goal is ultimately treating just a partial avenue of a widespread problem of "get around the character limit" abuses. I don't think it causes a substantial enough effect to help us that it would warrant implementation. As far as limit evasions go, this one is probably one of the lesser used, and moreso the lesser used in terribly bad fashion.