Earlier quoted context omitted.
I don't think the MacBook [Pro] is a flattering comparison. Apple is rapidly falling away from their traditional simple and obvious product lines, and the current MacBook lineup is extremely confusing to a lot of people.
Having a new "MacBook" that's thinner than the "MacBook Air" is admittedly a bit weird, but it's a transition period. Once the price on the new one goes down, they'll drop the Air from the lineup, and it'll just be MacBook vs MacBook Pro again.
The MacBook Pro Retina 13" is almost the same weight and size as a MacBook Air 13". It no longer makes sense to keep the Air around as a "lighter" alternative.
IMHO, both the Air and the non-retina-Pro are going away. Keeping just the MacBook and the retina-Pro is what makes sense the most (the rest are just cheaper alternatives, and Apple doesn't generally do cheap).