Well, if you think that IBM, Cray, Fujitsu etc are being silly making supercomputers and should start making phones instead, feel free to suggest it to them ;-)

The point is that there's nothing inherent in the ARM ISA that makes for better energy efficiency compared to any other architecture (or if there is, all implementations so far have been incredibly bad and wasted that advantage).

Your OMAP-based handheld may last longer than your Atom netbook, sure, but that's because the rest of the system/SoC is designed to conserve energy well, particularly when idle. A PC is a terribly wasteful thing because it has to comply with 30+-year old design decisions in order to run software that expects them. An x86 (or even better, x86_64 or x86_32) system does not have to be a PC however. Remember the original Nokia communicators for example? i386s.