Did you, perchance, happen to read the long quote from Mark Evanier on precisely this topic I posted the day before yesterday? If not, I commend it (obviously, I posted it).
I'd say that, in general, the ratio is probably more 50-50, or higher, but I believe people have a remarkable capacity to talk themselves into believing things, particularly since it's a positive feedback cycle when they're prone to seek out more material that agrees with that position.
It's definitely show business. Rush worked in radio for many years before he stumbled on the gimmick that worked.