Tong Family

Why build a 13-inch Retina MacBook Pro and not a Retina MacBook Air? | 9to5Mac

It turns out there are a few reasons, but let’s start with the Retina display: the Retina Display on the 13-inch MacBook Pro will be 2,560-by-1,600 (for those scoring at home, that resolution is the same as the discontinued 30-inch Cinema Display) and is certainly a lot of pixels for a mobile video card to drive. Sure, the Intel 4000 series chips currently powering MacBook Airs can drive that many pixels; but if you have ever hooked your MacBook Air up to a 27-inch or 30-inch display, you know it is not a good way to live your life —especially not for ‘Pros.’
So…to drive a 2,560-by-1,600 Retina Display, you need a discrete video GPU which requires some extra room on the motherboard and some extra battery power to maintain mobile usage benchmarks. Much more of each than an Air can currently hold.