If you look at Lenovo, the world's largest PC manufacturer, they don't make a 13-inch consumer notebook. They offer a few specialty 13-inch business models, but the vast majority of their lineup is 14-inch. Ditto for the #2 and #3 players, Dell and HP.
It's clear 14-inch is the sweet spot between portability and productivity. PC manufacturers realized this years ago and I doubt Apple is unaware.
Apple being Apple, they're not going to offer what most consumers want at a low price, otherwise who will pay for the MacBook Pro? We see this same strategy with cameras in the iPhone lineup.