Big egos can be found throughout all societies around the world. It is just those who make a living in front of cameras that have theirs exposed more often than most.
For the most part, I think actors and actresses have always considered themselves as professionals no different from any other working in industries outside of entertainment. However, I do also believe the projects they work on are the main factors that brings out the best in performers. A substandard or unmotivated director will not push actors strongly enough. A crappy script can be only improved upon so much by performance.
I think actors and actresses do deliver their best work in most situations though. Awards simply feed their vanity, just as it does for other people too.