Ditto. Although I've heard it similarly...
Top third = academics/attendings/researches
Middle third = best clinicians
bottom third = make the most money
the idea is that those who gun for the top positions get the most prestigious (yet, often worst paying) academic positions as they are the best at studying/memorization/everything else it takes to be at the top of one's field (intellectually).
The middle third, while less inclined intellectually, often meet the balance of "focus on academics" with being good at "life." They identify with their patients better than those at the top, but are often more clinically inclined than their peers at the bottom. They also will go into academic practice, but not as often as those at the top of the class.
The lower third, while lacking in academic skills, make proficient clinicians (due to the rigors of training), but often have a more rounded skill set (i.e. they're better at running a business, sales, patient interactions) than their peers. They're also the least "academic" of the group, which means they're the least likely to go into academics, which again usually suffer in pay.
...but that's just my opinion, I could be wrong.