My understanding is the change from R12 to R134a was because DuPont's patent on R12 was over, and DuPont lobbied hard to get R12 banned in the USA (it's still used in other countries like Mexico) and offerred R134a instead.
The pharmaceutical companies are basically doing the same thing once a patent runs out, and generics are on the horizon.
They'll lobby hard to keep their marketplace by releasing basically the same drug but with slightly different chemistries (e.g., slow release, etc.) and lobbying hard to the Doctor's office including loads of free samples.
The WallStreet Journal had a good article about 2-weeks ago. They'll even begin filing for patent's for any variation so that genrics are even harder to produce.
It's one reason why generics aren't widely available for the "designer" drugs, and Health Care Insurance for these drugs have gone up in premiums.
1988 360TE AMG