While I'm no expert on digital projection, here is what I understand about the difference between 2K and 4K resolution (aided by Jette's post about digital restoration): 2K is the current standard for both digital cameras and digital projectors. The amount of (picture) information offered by 2K is less than the amount of information offered by film and film prints. 4K offers twice as much information as 2K and it more sufficiently represents the quality of film. While 4K cameras are currently available, most digital features are shot with 2K cameras and most features shot on film are digitally scanned using 2K scanners. So why is it so important for Landmark to have overqualified projectors?
Landmark is co-owned and co-run by Todd Wagner and Mark Cuban, the duo that also operates HDNet (and HDNet Films and HDNet Movies). Through HDNet, Wagner/Cuban is currently producing 4K content, which they will be able to distribute to their 4K projectors, as well as to non-theatrical 4K media (like Blu-Ray, HD DVD and HD television, presumably). Cuban also points out that they are simply preparing for when 4K content becomes more common. For now, though, Landmark patrons will only be able to appreciate 4K resolution in the form of pre-show materials provided by Sony. If Wagner and Cuban are smart (which they certainly are), they will also hit up Warner Bros. for newly restored 4K versions of Blade Runner, Cool Hand Luke and Bonnie and Clyde to screen as part of their midnight movies selection.