The bottom third thing is often true in law but not as much in medicine-it is more like the bottom 2/3rds make the money. The top 1/3rd goes into academia largely and makes jack. THe upper-middle third usually are those getting good-great residencies in good fields and the money-making fields-cards, gi, cardio surgery, optho etc
Bottom third go into a variety of things but almost always do private work rather than any academia and any american who ventures into the market with a skill can make tons of money.
You're forgetting that fields like cards, GI, cardio surgery (MONEY making fields) actually DON'T even look for one SECOND at your preclinical grades. Your performance in residency and institutional connections are MUCH more important. At BU, if you do IM residency here (fairly easy for a BU grad), you're pretty much GUARANTEED a cardio or GI spot here. Same goes for the local state school UMass. IM spots at these two schools are not very difficult to attain. As for CT surgery, that comes after Gen. Sug, which is not nearly as competitive as the surgical subspecialties.
That bottom third thing...I don't know where it comes from. But I do know that if it's money you're interested in, then you'll do what it takes to make that money. If you're interested in a specialty and more of a pursuit of happiness, you'll get that.
My dad is an FMG. He's making a ****load of money in a community hospital. His friends are FMGs. They're the richest people I know, driving their freakin' mercedes everywhere, having the big houses. Clearly, these people are much more status conscious (sometimes it's cultural) and have made certain sacrifices for big money (ie practicing in crappy, underserved areas doing work at small community hospital). But they're getting it done.
So bottom line is, if you're business savvy and smart, and you want to make money, you'll find a way to. And generally, in my experience, those guys who work their assess off and finish at the top are excellent doctors and scientists, but aren't very smart business wise.
The doctor I know with the most diverse career and who makes the MOST CASH at the end of the day is a GI doctor. He's an FMG, failed boards in the 80s twice before passing, got a crappy IM residency, failed IM boards in the 90s before passing, then SOMEHOW after sheer persistence, making connections, and working his ass off, got a crappy GI fellowship in some low-level VA hospital. Afterward, he opened his own practice, built a massive building that housed his own endoscopy suites (read: no facilities fee for endoscopies), hired three GI doctors just out of fellowship to work with him, and basically paid the building off in two years simply on endoscopies. Rented out 2/3 floors to primary care doctors (who paid HIM for the building space and sent HIM referrals cause it was easy for them).
The man wasn't book smart, but he was a genius when it came to money.