On it's own, cable length may be a small thing, but added to all the other 'little bits', can add up to quite a noticable difference in the end.
Some manufacturers use 'dual mono' layouts in amplifiers, as well as 'same length' channel tracks on circuit boards, and Naim match components like capacitors and resistors that are common to both channels - little things which are extremely minimal, and costs money to do, but just eek out that little bit more from the component.