Maybe the Air is on the way out, being replaced by the iPad? The new one is called iPad Air after all..
With the recent price cuts and other changes to make the MBP more appealing to the general public instead of power users (no way to upgrade it, integrated graphics, thinner/lightweight), that seems like a reasonable strategy in a post-PC world.
I don't think so. The Air was only updated a few months ago. More likely that the battery technology just hasn't got there yet- the Air doesn't have the space for a battery large enough to power a Retina display.
2+ years later and still no retina macbook air.
... since that is the only relevant datum here.