TBH I'm not entirely certain why Chord make a specific version of their ethernet cable for the Meridian speakers, unless it is to save cost.
Cost might be a consideration as the low-speed serial connection that controls the speakers (as opposed to the signal pair transmitting the music) doesn't have to be done with ultra-expensive wire, however I'm not aware of Chord offering a SpeakerLink specific cable at a lower cost than its ethernet equivalent. Unless I'm missing something, SpeakerLink was designed to work over CAT5e and other ethernet cables, such as the AudioQuest Diamond, also bring about a definite increase in sound quality (albeit at a cost).
PS It dawned on me, while writing this, that Chord might try and tune their SpeakerLink cable for the lower frequencies used by SPDIF compared to ethernet, but I haven't seen them make any comments along these lines.