A couple of comments here:
Well "vet" food is not prescription per se, there are certain foods i.e. Medical - that are only available through vets. And yes, for sure, they get terrific profit margins on it. But it is not prescription only.
But as a pet store owner, even though I might supply an alternative and less expensive food that might solve the same problem, I do not do it - simply because I'm not a vet. All I can do is supply questions back to the pet owner to arm herself to ask the vet about the food.
I really worry, frankly about these vet foods because the primary ingredients are crap. When Bacca was diagnosed with his various illnesses, by Vet suggested that I look into a K/d diet medical diet. Why, I asked? She said because he needs a lower protein. I pointed out to her that the main ingredients were garbage. She basicly said, yes, you are right. I'm a vet, not a nutritionist!
All to say, if your dog has a condition that is being treated with "vet" food....do yourself a favour and find out what the vet food is supposed to be supplying to your dog and then google away to see if you can find a "non-vet" food that does the same.
That being said, the behaviour of that vet is unacceptable. I would report that vet to the Ontario Vet Association or whatever they are called. If nothing else, they should have taken your dog as an emergency patient or referred you to the city's emergency vet clinic. I think to refuse treatment should be subject to losing ones vet license.