I do think part of the reason that health service companies and insurance companies adhere to HIPAA is because it helps them keep their customers "locked in" to their product. It is often used as an excuse to prevent the digital transmission of health care data from one provider to another ("they gave me a CD with my data to give to my new doctor") and to prevent people from leaving "the network". These are companies that have very real incentives to avoid sharing data with each other, indeed, the more data each holds hostage the more powerful it becomes (hence the consolidation in the field).

That seems very different to me from how advertising companies function and make money.