The fact that the iPhone 5 didn't contain a new industrial design concept and instead only increased processor power and screen size while reducing device weight and increasing battery life* while upgrading network speed prompted a fair amount of commentary about the slowing pace of innovation at Apple. But it seems about 2 million devices were preordered within 24 hours, and now even if you preorder, you can't actually get on on launch day.
The iPhone 4S, which, as I recall, was also "disappointing," got about 1 million preorders, which itself was a record. So clearly they're doing something right. I think what you'd actually see is that a lack of technical innovation is what would induce a change in industrial design as a way to artificially gin up excitement. The new iPod Nano seems to me to be in that spirit. It's a declining product in a declining market segment that they couldn't come up with any interesting new ideas for, so it got a basically arbitrary new design because—hey—why not?
* Correction, Sept. 17, 2012: The initial version of this item omitted the word "increasing" when describing the change to iPhone 5's battery life.