Your point is well taken. I see logistical hurdles, though, the chief one being that if one makes that statement once, most people who read one's posts will never see it. They won't know to go looking for the place where it appears, or won't care enough to make the effort.
As far as comments from doctors, I do seem to recall seeing posts that say that, from time to time. I didn't bookmark any of them, unfortunately. When I first interviewed the doctor who ended up as my PCP, he said (unprompted) during the conversation, "I don't know everything." That's one of the reasons he became my GP.