I love the turn of phrase, but given this new display manages to improve on energy efficiency, I'm suspecting another, more mundane consideration: the Dread Marketeer. As is, the Pro line has the retina displays, whilst the Air doesn't, thereby setting out a clear product line delineation. (Not the sole one, to be sure. But, if Apple wishes to continue the Pro/Air distinction, this would seem one quite noticeable parameter)
For Air-like sizes, the GPU matters very much - even if the screen takes less wats, it takes much more GPU power to feed it, and that would hurt battery life.
