Who needs it?
Leaving aside the obvious marketing benefit of "Bigger, Better, Faster, More", let's step back for a second and consider.
There seem to me to be two types of laptop user: those who primarily want to watch videos and everybody else. For the video-watchers, the 16:9 format is ideal but for everyone else it's terrible - especially for "business" users who deal mainly in A4-portrait format documents and people who surf a lot, as most websites are STILL designed for tall-thin, "page" form factor web content.
So we have a whole generation of laptops that are optimised for watching TV and films - oh and playing games maybe, to the detriment of everyone else. Now unless those media consumers are watching their shiny, glossy screens in perfect darkness the quality of what they see is always going to be compromised: by glare and reflected light.
So given all that, you have to ask: can yer average lappy user benefit from sooper-dooper screen technologies and resolutions that need an electron microscope to view adequately? Given that there's been no real drive to improve laptop screens since the early days (my 1996 vintage Olivetti sported a 1024x768 screen, I guess that would be "HD" by today's standards), I can only assume that the current crop of high resolutions is only being marketed on a "becauwe we can" basis as part of the BBFM principle.