I'm not sure about this, though I guess it's big business for these companies.
However, I went today to see an independent vet in France to sort out the dogs' paperwork to come home. One of the dogs had been vomiting yesterday, (don't ask, he's a scavenger), and he was given a thorough examination - teeth, ears, eyes, heart, temperature - then he was given an injection and a big bottle of medecine. I was happy to accept the extra treatments and drugs in order to improve the outcome speedily. I was also fully expecting a rather large bill, we were in the consulting room for 40 minutes. The cost was only 112 euros, that's £95. I'm sure it would have been double that amount in the UK at my CVS vet. It's £60 per dog just to walk through the door, and the medicines often cost as much as that again.