A few other mobs drop off-the-beaten-path trade goods from skinning (e.g. Devilsaur Leather and scorpid scales), but AFAIK, only the Silithids in Silithus skin out vendor trash.

I'm not sure it was an error on Blizz' part, though.  In days gone by Silithus was endgame, and most of Silithus' weirdnesses (its potentially endless quagmire of quests, the huge sprawl of AQ40, the game of Silithyst) make sense in that context.