The smoky corporate board room full of selfish greedy bastards is about as realistic as the totally naive and apolitical scientist. Most scientist like money but the Nobel pays pretty decently and having one pays more, so even if their own motivation was only cash and social standing, and it's probably not, they have very little grounds to sit on a cure. Also, corporate CEOs aren't dumb, and would know they have just about zero chance of sitting on a cure, so even if their motivations were strictly cash and power, which they probably are not - people are people - they'd have to be dumb as a doorknob to think they could sit on one, and much like science, a certain amount of intelligence is generally helpful in ascending to the top of a major corporation. Secrets get out, and everyone knows it, unless everyone who knows has a strong motivation to keep them secret, which would be improbable for a big project group, and even then secrets tend to get out.

So no, I don't think there are cures to diseases hidden away in the warehouse from Indiana Jones, and I don't think you're being to cynical, I just don't think this concept has much logic behind it. Same with the water-powered cars or all those other wonderful things secreted in the Indiana Jones Warehouse.