And a certain attitude contributes to that... he once said something to the effect of "Any airplane will do whatever you want it to do... if you ask nicely".
What's also implied there, I think, is that you must be aware of what it can do. So many accidents are caused by trying to fly airplanes by force of will, wishful thinking, or by the pressure of the pilot's agenda. But once you know the envelope, you have to be gentle poking around in the corners. Just look at Hoover finessing a Sabre through some very slow, graceful maneuvers... not part of the intended mission for a high-speed interceptor/dogfighter, but he knew it could do it, and he just "whispered" the damn thing. One moment very precise, the next playful, but always apparently well ahead of it. One of my favorite airshow clips ever...
http://www.youtube.com/watch?v=TRt6UnNzR6I
As for the "fearlessness" theory, I doubt that highly. I think one reason old-school fighter/test/show pilots like Hoover and Yeager have lived so long is because they have enough sense to be scared when they should be.
Courage can't exist without fear...
it's about staying focused and doing what you need to do when you would rather curl up in a ball and cry for your mama.