It’s a lot easier to write “Vicodin 5/500” than it is to write “hydrocodone/Acetaminophen 5/500”. Even then, I don’t expect them to dispense the name brand, though.
One reason I believe sticking to the same pharmacy is a good thing is that it helps them know everything I’m taking–and also that they know my doctor which means everyone is on the same page, so to speak. If I’m Dr. Y’s patient, and for whatever reason he or she determines that I should use a controlled substance, and I bring you the script: does that mean you’ll refuse it, or just that you’ll check up with Dr. Y to make sure it’s valid? I thought you had to do that with controlled substances anyway.
To me, as a lay person, the generic names of some drugs sound a lot more fearsome, as it were, than the brand names. For instance “amphetamine salts” sounds a lot more troublesome legally than “Adderall”, which may be associated with hyperactive children, and therefore with mild stuff like childen’s Delsym and so on.
Myself? If I had any doubts, I’d call first. If the doctor (or more commonly his nurse and/or medical assistant) verified it as valid (and you weren’t doctor shopping and on 4 other potential respiratory depressants…you get the idea), I’d fill it without a single problem and probably even an apologize to you for taking the extra time I needed to verify it.
Eh, I often refer to the drugs by their brand name myself. It’s what the patient knows and can say. I’m not there to insist “Oh no, you HAVE to use the proper generic name since that’s what you received. It’s triamterene and hydrochlorothiazide.” It’s easier for both of us if I just call it generic Dyazide.
Could you convince your Endocrinologist colleagues of that? 
Seriously though, if a patient comes to me on brand name Synthroid/Lanoxin/Coumadin/Dilantin, that’s what I dispense to them, unless they want me to call their doc to see if they can switch. More often than not, the doc is fine with it, provided I caution the patient that more frequent blood level monitoring may be required until their generic dose has stabilized. Other than those four drugs, there aren’t many retail drugs that a brand/generic substitution makes any difference based on the studies I’ve seen (arguably Neoral vs Gengraf, I suppose).
Regarding the “magic words” in Arkansas, according to the pharmacists I’ve worked with, we don’t require “Medically Necessary”, but the “DAW” or equivalent has to be written by the doctor, no checkboxes or computer-printed stuff. And we override it for the patient if the doctor doesn’t play by the rules, especially on silly things. And it’s even better when we get a prescription for something that says “Lipitor 40mg DAW” or something, there was an APN near the last store I worked at who would do this sort of thing all the time.
Another LONG story - walmart has introduced a policy over the last year that says that if we are going to dispense a non AB-rated generic, we have to call the doctor for permission. Short story - if a drug is rated as “AB”, it has been tested to be bioequivalent to the name-brand, but the FDA only started requiring this (fairly) recently, so there are some drugs on the market that were grandfathered in, and for some reason, there are also some drugs that don’t have an AB-rated generic on the market, like Mepergan (although that’s a bad example since the generic isn’t available anymore, I don’t think)
BASICALLY, it means that if you bring me a prescription for certain things that have been on the market for long enough in generic, or some of the funny cough/cold medicines (NOREL DM AND DALLERGY I’M LOOKING AT YOU!!!), we have to take time out of our day to call the damn office, document the authorization, and rescan the prescription, while you are confused about why no other pharmacy in the world does this, since it’s not required, and sometimes it takes two days for the doctor to call back, at which point we just give up and fake it, and hope that the goonies at home office don’t come after us.
Rant over!