If you go to a pharmacy as a human patient and pay for your rx, you are paying an upcharge at the pharmacy (or your insurance is). That upcharge includes the pharmacist's expertise to be sure that your doctor is prescribing the right med, dose, etc. After all, the pharmacy and pharmacist has to make money. Human pharmacies do NOT have veterinary knowledge.
Now as a vet, you sell the drugs in your pharmacy at an upcharge... to include your expertise in knowing what drug, dose, etc to give that dog/cat for that disease condition.
People so often think... you are just giving me an antibiotic.. anyone can grab an antibiotic off the shelf why such a large cost? Well, sure, anyone can grab an antibiotic off the shelf and give some to their pet. But the vet knows what abx has the distribution to get to that skin infection, what bacteria are most likely to be present on that skin infection, what abxs will kill that bacteria as well as what dose is needed and is safe for that species (time dependent vs. concentration dependent abx). So when you buy your rx at the vet clinic, you have paid, in part, for that expertise. And the vet should be rightfully compensated for that.
Now, when the owner asks the vet to write an rx, the vet is no longer being paid for the expertise in knowing what drug to give, the dose, etc. So now you come up to should the vet charge for their knowledge? Which if every person in the world were smart and recognized what they are actually paying for the answer would be yes. However, people are irrational and don't recognize that they are actually paying for a service when that vet uses their knowledge to write an rx for their pet (that knowledge that cost them... oh $200K).
So this is one of those gray areas... can a vet charge for that? Yes. Should they? Well, up to them. I personally wouldn't but only because people are irrational.
However this does bring up another point... if vets are going to be writing more and more rxs, which seems to be happening... are prices going to go up elsewhere to cover the cost of them prescribing meds? Maybe. You could see increased exam costs, which would suck because not every patient coming in needs an rx.
Just my thoughts... which aren't worth much at all.