The Newsweek article quotes Gavin saying he and others were convinced Satoshi was a single person, based on how his code was written.
I believe it was a single person as well. The kind of genius expressed in the original Satoshi article and then implemented doesn't get invented in committee. Even if you had 10 men the equal of Satoshi and put them together on a project to create bitcoin working together, you'd find them bogged down and disagreeing with each other. They'd never get it done. Some things just need to be done by an anti-social "jerk" working in a closet, or they never get done at all. Looks like that's how bitcoin came to be.