I, too, can't speak specifically to ICN-LAS, but click here http://http://www.flyertalk.com/forum/delta-skymiles/1198446-korean-air-totally-blew-my-mind.html for my experience on a recent flight from JFK-ICN.

In a nutshell, the service is excellent. Not all routes fly the same seats, but on KAL's website you can see which seats are operated on which routes.