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.