I'm sure that companies hold back innovation across all sectors of the economy to one extent or another. Companies don't do things for the good of man, they do them in the quest for profit, and you don't want to interrupt your existing income stream if you can help it.
However, in a competitive marketplace, a drug manufacturer that cures things is going to win against competitors that don't. As such, I don't suspect this idea is as widespread as some of you might think. And academic and government researchers worldwide are at work on these things alongside private industry. Not all of these researchers are going to benefit by failing to cure disease.