MD's/DO's have unlimited scope of practice, so they can pretty much write for whatever they want. There's no logic whatsoever to "restricting" specialists to prescribe in their field of expertise. It's idiot pharmacists who make up fake rules that make the rest of us look dumb.
That logic would basically mean an internal medicine physician/GP can write for whatever comes up in clinic, but when he/she goes to complete an infectious disease fellowship, suddenly they can't prescribe anything except antibiotics/antivirals?
That's stupid.
On the other hand, if you have a young hospitalist attempting to treat MRSA infected hardware with clindamycin, as a pharmacist you have to identify that he/she is in over their head and intervene. Just because a trauma surgeon doesn't readily know the average starting dose of a beta-blocker, doesn't preclude them from being able to prescribing one. It's all fixed with some simple peer-to-peer communication.
Being a little bitch about it and trying to shut down prescribing rights is infantile and a disservice to your patients.