I made the above point recently in response to an article bemoaning Microsoft’s improved high resolution screen handling being limited to the Metro interface only. I figured I’d reiterate it here for emphasis.
The reason small high res (e.g. 2560×1440 at 10.1″) mobile screens work is the fact that they’re handheld, which makes viewing tiny pixels easy. Try doing the same thing at desktop monitor range and you run into problems, mostly vision limitations.
The point of traditional large high res screens (e.g. 2560×1440 at 27″) in desktop usage is not to increase the number of pixels per element, but to allow more elements on the screen so that users can work with multiple applications/windows/documents simultaneously.
Combining the above 2 points: the motivation for high res is different for mobile as opposed to desktop. For mobile, it’s about close range visual crispness of the same amount of content shown on a lower resolution screen. For the desktop, it’s about showing more content than a lower resolution screen, period.