I think a definition of task vs work is needed. A task is something the dog does to mitigate the disability that can be easily demonstrated on command. For example, picking up a dropped object is a task. Work is something that the dog does to mitigate a disability that can not be easily demonstrated on command. For example, altering to a medical condition can not easily be demonstrated as there has to be an episode occurring for the dog to alert. In either case, the dog has to DO something. Just being there making a person feel better does not count because the dog isn't doing anything.

The ADA says that the dog has to do work OR task, and only one is necessary. This is an issue not just for PSDs but also for Medical Alert dogs. My dog is a syncope and seizure medical alert dog. He does have other tasks as well, as most dogs will, but the absolute most important job he has is his work in alerting.