Power Meters / Powermeters (SRM, Powertap, Quarq, Ergomo, Vector, Stages, power2max, P2M, 4iii, InPower, Cinch)

According to this: http://djconnel.blogspot.co.uk/2012/09/interbike-2012-crankarm-based-power.html they could measure the twist if they measure in different locations. Do they do this?

I don't think they can instrument the crank in enough places to isolate usable torque from all the other force components which are deforming the crank within the small area of the back of the crank to which they stick their device.

And if I'd seen that blog post before, I could have saved myself a lot of time by just linking to it instead of essentially rewriting the same thing from my perspective :-)