The transition from proprietary architecture to open modular architecture just happens over and over again. It happened in the personal computer. Although it didn't kill Apple's computer business, it relegated Apple to the status of a minor player. … You also see modularity organized around the Android operating system that is growing much faster than the iPhone. So I worry that modularity will do its work on Apple.

"Why Clayton Christensen Worries About Apple" in Forbes (7 May 2012)