I have myself taken store reptiles to my personal vet (at PetSmart's expense). Recently the corporation has made a rule saying everything must be approved by the district director BEFORE taking to a vet. So basically we're having to go up the chain of command just to get the buggers to the vet. If you have a district director more interested in saving the $1000 vet bill each PetSmart is allowed every month (and thankfully, that's not a concern at my store), only the more expensive birds will be going to the vet.
I can't speak for all the stores, but at mine, we take all animals we suspect are ill off the floor for treatment. Then again, it helps that we're all very vocal and bull headed...We won't take "no" for an answer when it comes to our charges. Then yet again, no one under the age of 19 is in our department to muddle things up...