I have never personally found a cure to any disease, so I can't say for certain. That being said, it wouldn't surprise me at all. The drug companies would definitely prefer Drug A in that situation.

The real question is, how much research is being put in to treatments versus cures? The big drug companies skip the hassle of even having to throw away a cure by simply putting their research in to disease treatment. Most if not all of the projects these companies work on is in the search for treatments, not the search for something to cure them.

It's a perfect system for them; no one can afford to do research that is interested in curing the diseases.