I think your reasoning is sound. Would you be comfortable broaching the subject based on what you feel would be helpful for you rather than as a challenge to the policy? Basing it in your own thoughts about your treatment might feel a little less confrontational. Plus, I think any t worth their salt would be encouraging of self-advocacy (even if they're not willing to change the policy).

The original question...I don't even know if my t has a cancellation policy.

I'm curious- Surely your t has got some kind of illness exception?
My massage therapist just changed the 48-hour cancellation policy to state very clearly that illness is an exception and please don't bring us your germs. People were showing up quite ill to avoid paying for a missed appointment.