During Apple's quarterly earnings call today, Apple CEO Tim Cook admitted that the company made some miscalculations about consumer demand for the iPhone 5S and iPhone 5C in North America. "It was the first time we ever ran that play, and demand percentage turned out to be different than we thought," Cook said. Apple doesn't break out individual sales figures for each iPhone model, but Cook made it clear that the iPhone 5S has thus far proven more popular than the cheaper 5C. "The mix was stronger to the 5S, and it took us some amount of time to build the mix that customers were demanding.”

Cook offered up one theory as to why that's the current trend. "I think the 5S, people are really intrigued with Touch ID," he said. "It's a major feature that has excited people. And I think that, associated with the other things that are unique to the 5S, got the 5S to have a significant amount more attention and a higher mix of sales."

But Cook's careful assessment seems to confirm that while the 5S is seeing extraordinary demand, the 5C may not yet be meeting Apple's lofty expectations. Cook said one bright spot was a "new to iPhone" development: the 5C isn't as popular as expected (at least relative to the 5S), but it's excelling at bringing new customers to iOS. It's also faring better than the 4S did when it occupied the middle slot of Apple's iPhone lineup. In regards to the pricing structure, Cook said only, "If we think it's in our best interest to make a change, then we'll make one." Apple's line in the sand, Cook said, "is making something that's not fantastic." All in all, Cook concluded "I think last quarter we did a tremendous job, particularly given the mix was something very differently than we thought."