[Ellie May]

Some of this is vet preference and there may not be one right answer.
Yes, for most surgeries, Iso or Sevo should be used. IMO, using those two injectables for a spay and no gas is not okay. However, most vets that use gas knock down with an injectable or IV drug. I don't know a whole lot about these, but some are better than others. I do know that phenobarbrital and euthasol are not okay. Some people have a problem with ket/val and to each their own, but I think there needs to be a little bit of room for vets to do what they are comfortable with. Each drugs works differently and some vets choose certain drugs based on that. Some will mask down with gas, while others say they isn't as safe as using an injectible first. Propofol and then maintaining with Iso seems to be a good way to go as far as I know.

Gas anesthesia is more expensive and some just don't want to cut into profits or don't want to raise prices.

Most vets I know of don't really suggest preop bloodwork for young, healthy animals. That wouldn't stop me from going to them, but if I requested it and they told me to skip it or it was totally unnecessary, I wouldn't use them.