Would America Online, Gold's Gym or other types of monthly membership services billed to a MasterCard/Visa debit card number be considered a Preauthorized Transfer under 205.10?

If these are considered pre-auth'd transactions, how are other banks compling with 205.10(c) to stop future transactions from hitting the individual account without having the transaction post, then chargeback after it already occurred?

Yes, assuming the card is attached to a consumer asset account subject to Regulation E protections.

I believe that MasterCard and Visa both have blocking services that address exactly the scenario you've described. There is undoubtedly a fee, but it is probably less expensive than the cost of the time involved in trying to recover funds through a chargeback.