Haswell will fix this. Microsoft does well when it designs for next year's hardware - sell to the enthusiasts, then wait for the masses to upgrade into their maw.
The main difference between the RT (10 hour life) and the Pro (4 hour life) is the CPU, isn't it?
A peak 17W vs 10W draw is a pretty big difference. And that's peak power; Haswell may be even better at idling. We might see 6 or 7 hours on the next Pro (wild guess).
