Apple watchers and techno pundits are guilty of assuming that everything Apple does is an instant success. The iPod was not an overnight hit, as Philip Elmer-DeWitt points out in Fortune:
It took the iPod 17 quarters to reach 30 million units. The iPhone did it in 10.
The trajectory is the same for the iPhone as the iPod, only faster. The iPod is approaching 250-million units sold, vs. the iPhone which is approaching 50-million units sold. Same trajectory, though.