I think that's only true if you're applying to a more geographically diverse school. If you were to apply to somewhere pretty competitive, you'd have to be extremely qualified for it to be a "wise" decision (and even then, depending on the school, it's doubtful).
But in other cases, early decision works to make up for a slightly weaker application. One of my state schools works this way, I think the main people who apply early are those below the school's averages. I mean, it makes sense (just like it does from the college perspective), you guarantee you're filling spots now to slightly "diminish" your student body later. If you're a state school looking to fill seats with predominantly residents, if you only let residents apply early, it works towards your goal.
To answer the thread, an adcom told me about a student admitted with a 19. I think he ended up failing a lot of stuff his first year, though.