Not necessarily. Yes, if you're fortunate enough to have something like Trac that can easily link between a line of code and a ticket number, then bug reports

Not necessarily. Yes, if you're fortunate enough to have something like Trac that can easily link between a line of code and a ticket number, then bug reports can handle everything. But otherwise, how would you describe it? Sometimes a problem only "makes sense" if you're looking directly at the affected line of code, and the comment is right there. If you leave a 'grep'-able thing like "FIXME" in your comment, you won't really lose it.