^ This. People have no idea what they are asking for when they "want" a "retina" display. It's based on your distance to the screen.
Also it's quite possible to implement. The sony Z series has a 1600x900 13.1 inch with optional 1920x1080. But again until they change resolution dependance in OSX, which should actually be coming it will work well. Also the Z has decent battery life also.
The main problem is cost. Apple takes a completely reverse approach to laptops as most manufacturers.
ie most PC makers make 15.6 inch their cheapeast junk model, ie 400-500$, and you pay more to get either a larger (17 inch) or smaller (13 inch model)
So companies like sony make small machines but make it much more expensive for the same specs (given the costs of implementing the high res display on a small laptop, weight, power, cpu/gpu config etc.)
Apple on the other hand prices it's laptops on a bigger is better perspective, so the 15 inch is always better than the 13 inch, and therefore the 13 inch will be cheaper.
I actually would prefer that apple kept the macbook 13 inch their low cost laptop, and actually made the 13 inch pro "macbook pro" spec matching the rest of pros. Now it would have to cost alot more than the current price and be near the 17 inch in terms of cost, but it would be far more capable than the current 13 inch.
