1366x768 in 2014?
Edit: Also, that's the 11", I doubt they can squeeze many more pixels in there before it becomes unreadable. The 13" is 1440x900, which is more reasonable (I'm using it as we speak, actually!)
There are other considerations too. Phone usage patterns are way different to computer usage patterns. The vast majority of phone usage occurs in small blips of activity during which execution can be optimized for the CPU to race to sleep state as soon as possible. Computers don't have the same usage patterns at all, and have a legacy of first and third party software (on all major platforms) that have not yet been optimized for performance.
About your edit: remember that how Apple does it in the "Retina" models is increasing the definition, without affecting the actual size of the UI elements.
I would buy a "Retina Air" in an heartbeat.
I have the 2012 model, and it is an absolutely superb machine, but the lack of vertical pixels is its weakest feature. Reading documents is far from ideal: it is distracting to read a wide-columned pdf with a relatively small number of lines on the screen, and the screen isn't quite good enough to allow much zooming out. There is a noticeable difference in the usability of the machine when my eyes are tired. A higher-resolution screen would presumably help on both counts.
Because the software is generally well-put-together and the touchpad is excellent, the resolution is not so much a problem for actively using software, creating documents and so forth. But scrolling around and zooming in and out has an overhead, which again, more pixels would reduce the need for.
Retina would be nice though.
Admittedly the market for high end powerful 13" laptops might not be that big.
Lenovo can fit most of that it in their 14" T440. I'm sure if Apple set a team of top engineers on the problem they could find a way to make it work.