Even though the latest MacBook uses the same size display as the last-gen MacBook Air, the displays are not quite the same. The Air, being a more premium product, uses a display that's more similar to the MacBook Pro than the MacBook. You'll remember in our review that despite being both made out of glass and visually very similar, the MacBook's 13-inch screen was of a "lower" quality than the 15-inch MacBook Pro screen. You can see that blacks are much blacker and the colour representation is much better on the Air.
However, the new MacBook is a bit better than the old MacBook in terms of brightness, but the LED backlighting adds a bit of a blue tint to blacks. The Air doesn't have this problem, and neither does the MacBook Pro. Minor differences, but it should help the decision if you're trying to determine whether a MacBook is "good enough", or if you should go for a MacBook Pro.
As a reminder, here are the MacBook vs. MacBook Pro shots. It should be obvious which is which.