If I remember correctly, when you check in to Club O the staff informs you of the charges for a lost key and non-returned towels. Frankly I had thought the charge would be applied if you wanted to take one home.
Also, when we returned towels no one ever counted the number returned, we just placed them in a large rolling container and told the desk staff the number of towels we wanted as replacements. Granted we didn't lose any, nor have I ever heard of any thefts.