But isn't it Windows fault that it requires a power hungry x86 CPU? You can run other OSes on multiple types of hardware and have your engineers pick the best hardware for the device's needs. Or you decide "We're going with Windows!" and now your engineers are trying to figure out how to stretch the battery long enough to run this x86 CPU. If not for Windows being stuck on one platform I don't think we would have ever had the Atom.
I don't think it's just Windows that encourages x86 use; it's also the fact that the ecosystem is richer for that chipset anyway (hardware compatibility for things like the webcam and card reader come to mind). If you decide to go with a linux distro on top of custom hardware, then you might have to develop drivers yourself, as well as build up some UI paradigms customized for touch. WebOS gives them a great starting point to do just that, so in the end their actions still look consistent with their goals.
Well, it's richer mainly because that's the platform Windows runs on exclusively (or near-exclusively; there are probably a few non-x86 Windows installs out there still) and thus dominant. If you had more competition in processor architectures I would expect that you would not have such an unbalanced chipset and onboard-hardware ecosystem.
Also, I'm not really sure why things like webcams or card readers would depend on processor arch; most webcams (even built-in laptop ones) that I've worked with interface over USB. Same with most recent card readers. It's not like they're plugged right into the FSB or anything.
The Atom might only use 2.5W, but the chipset to go with it uses 9W!