With last month's MacBook Pro refresh, one question that lingered was why the 13-inch MacBook Pro was still stuck with the same mediocre screen resolution. From Quora, a possible solution! One similar to why the iPad 2 didn't get a resolution bump: Apple's holding out for retina displays to make things easier on developers:
Apple may move the Macbook Pro line to Retina displays within the next 12 months, doubling the DPI. If this is the case, Apple may not want to increase the DPI of the current-model Macbook Pros because if Apple is trying to go resolution-independent it's much easier on developers if Apple simply gives them 4 pixels for every one they used to have, rather than resample bitmap images to ratios that aren't as clean.
That "double-high resolution" was already hinted at in Mac OS X Lion, and follows with Apple's strategy of keeping devs from having to rescale their applications any more than absolutely necessary. For the rest of us, though, we're likely a year away from the crisp MacBook Air displays reaching our 13-inch MacBook Pros. [Quora]