"expertise is usually a pre-requisite for real innovation". May Be. But many a times, being naive (and inexperienced) may make one to see and think differently.
Are there people who innovate out of whole cloth? Maybe. I can't think of any offhand but I'm sure they exist. But they're not representative. Representative are people like Larry Ellison, who build an innovative company like Oracle (it was cutting edge in its time) by leveraging substantial industry experience and theoretical developments.