I don't vaccinate my dogs for either lepto or bordatella (and I show them), but I agree in principle. I understand most breeders have been burned by buyers who lied to them to get a puppy, people who don't live up to promises, but even so, we buyers have the right to walk away, and I think that's what we need to do rather than mislead someone in order to get a puppy.
If a breeder is determined to only let their puppies go to people who agree with their vaccination (or any other) regimen, they can certainly require that, but they then undoubtedly need to breed few enough puppies so that they can find people willing to comply -- and accept that a few will make the commitment and then violate it when their vet advises otherwise.