What these guys who would be considered mean have in common is they all made difficult decisions for the betterment of the company and many of those decisions came with a very high price (eliminating competition meant alienating lots of potential future employees and firing anyone who dared present an opposing viewpoint meant taking away their ability to provide for their family).
What would have been the results if they had been nice instead? Perhaps they wouldn't have been nearly as profitable or perhaps revolutionary products never would have existed because they wouldn't have had the drive to push people to their limits to create something great.
On the other hand they could very well have done just fine and been more successful but what they do know is what worked for the people before them was working for them so there's no reason to stop doing it.