ARM family CPUs are 16- and 32-bit processors (and soon 64-bit) whose architecture allows them to operate at very low power drains. Battery life, where operating systems and apps are optimized for ARMs, can be long. Charge cycles over the operating life of the unit where the ARM CPUs are used are reduced, people are happy. They don't really care what's underneath the hood, so long as they can do their work and entertainment on the device. Maybe 1 in 100 smartphone consumers can tell you what kind of CPU is in their phone, but probably more than half can tell you what's in their desktop or notebook. The CPU marketing identity war is a non-starter in mobile devices.
But it's Apple that now tells Intel what to do, as in cut the power crap. The initial Core-Duo chipset has been fabulously powerful, and only iteratively more scrupulous about power consumption. Operating systems are getting greener by loading fewer tasks that need to run all of the time, and video/GPU makers have become zealous regarding the power needed to make hungry display electronics more efficient, too.
And today, Apple's ex-CPU partner, Motorola (its mobile division) becomes a part of its greatest current competitor, Google. The silicon shifts.