@browncoat - It's not black and white though. They do tend to hold onto patents longer than perhaps they should, but as soon as they lose that patent the market is flooded with generic medicines and they lose their income. And that income is what pays for the development of other medications.
It's a very risky business, and it only works because of the huge amounts of money they can make. Millions are spent on developing medicines that may end up not doing any good at all, or may even be harmful. But those options need to be pursued or the right medications will never be found.