Nothing is "outright deleted with some regularity." The flag just puts the comment on a list that an editor looks over every day. We ban spammers who we find leaving links in comments, and occasionally mod down any egregious trolls that aren't already at -1. That's it. We've deleted comments in the past under legal threat but it's not our policy to do so normally. This comment showed up on the list but none of the editors are going to delete it. We think it's important to maintain a place where you can say whatever you want, even if that thing isn't popular or as in this case, correct.
"Little else matters than to write good code." -- Karl Lehenbauer