Sorry, forgot about Socceroos question.
That happens in MANY specialties. Specially when it means that another specialty comes with a much better way to diagnose and treat a disease better than the specialty that has traditionally managed that problem. That means that the bucks will move to the new or different specialty, and abandon the older "traditional" one. As I said this happens in many specialties, but since I'm more hip to those that deal with mine, I'll be limiting myself to those.
Example one:
Angiographers (the precursor of Interventional Radiology) came up with endovascular (and extravascular) techniques that were cheaper, faster, with far less risk and morbidity in treating a problem than were the Vascular Surgical techniques. In order to keep a hold on the available cash, several general and vascular surgeons started doing these techniques (I've witnessed the horrors that result). Some vascular surgeons get good at it and include it in their training. Like I said before, if you don't use it, you lose it. There is a host of endovascular procedures, and another host of vascular surgical procedures. Obviously, the vascular surgeon will never be able to catch up with the skill of an IR who does them several times a day, day in day out - while the surgeon does other procedures. The complication rates will be much higher than those of an IR - and nevermind about liability issues . . .
But the bottom line lies in where the cash and the future of practice will be. Thus, it will be no surprise to me if in the future (or today) vascular surgeons establish their own "endovasular surgery" fellowships to follow up on the techniques developed by radiologists. The result: two paths to the same fellowship. (But remember, if you don't use it as often . . . )
The similar thing happened with Neurosurgeons and Neuroradiologists. These two groups, on the other hand, have wisened up and have banded together to stop creating "parallel" programs. Between the two, they are developing standards for fellowship training in interventional neuroradiology. Both neuroradiologists and neurosurgeons will be training shoulder to shoulder in the same program in the same techniques.
But again, whoever does the interventional procedures the most will be the better one at it. If you keep busy on call to drain epidural hematomas, while another only comes to coil an aneurysm . . . and then, for one you need 8 years of postgraduate training, for the other it's 7.
Nuclear Imaging:
2 routes as well. One of them called Nuclear Medicine, the other Nuclear Radiology. They are EXACTLY THE SAME THING. For NM you train for 2 years after internship (if you want a job and a bright gainful future, you better have finished an Internal Medicine residency, and do NM as a "fellowship" - otherwise you'll be pushing carts and mumbling under your breath). For NR it's a 1 year fellowship after diagnostic radiology.
One does only NM. The other does NM AND MRI, CT, ultrasound . . .
Did I already mention "if you don't use it . . ."
NM is still justified because, honestly, it requires fully dedicated people to maintain a sizeable division of Nukes. There will always be a need for full time Nukes people.