Signed wavewolf! I don't think it's extreme. Being a dog owner I know how much my dogs don't like being left alone at the groomers. The difference between my dogs and a service dog is that my dogs don't go everywhere I go so they're somewhat ok with being left alone. I can't see it being the same for a service dog since they're so used to being with their companion and looking out for them. I don't see how being in the same grooming area can affect anyone. If anything it shows that they're trying to hide something that they don't want us to see and that's quite concerning!
DJ, It really depends on the groomer, too. When there are a lot of upset dogs there, it affects all the dogs. My service dog is pretty good about being left at places he knows, but any separation is hard on him and even harder on me! I get separation anxiety. The horror stories about grooming at Petco are numerous, so I would never leave my dog unattended there.