This simply isn't true - or at least it ignores half the issue.
For their performance, Intel chips aren't powerhogs. A i5 uses a lot more power than a Tegra2/A5, but is a lot more powerful.
An Atom use a bit more power than Tegra2/A5, but is a bit more powerful.
Intel is pushing Atom down into ARM territory in terms of power usage, and ARM is moving up towards Atom - and, to the surprise of no one who knows what they are talking about - the power usage at the same level of performance is roughly the same.
Arstechnica had an excellent article about this back when NVidia started talking about their desktop ARM push: http://arstechnica.com/business/news/2011/02/nvidia-30-and-t...
A good quote:
It's also the case that as ARM moves up the performance ladder, it will necessarily start to drop in terms of power efficiency. Again, there is no magic pixie dust here, and the impact of the ISA alone on power consumption in processors that draw many tens of watts is negligible. A multicore ARM chip and a multicore Xeon chip that give similar performance on compute-intensive workloads will have similar power profiles; to believe otherwise is to believe in magical little ARM performance elves.
Intel isn't out of this game by a long shot. For example (Intel powered) Chromebooks perform roughly as well as an iPad in terms of battery life. There is little evidence that an ARM powered Airbook would do any better if it offered similar levels of performance (unless you believe in the magical ARM performance elves mentioned above).