(Chero, 24.October 2014) There are several proven creatures that should sleep at night, http://www.wowhead.com/npc=50838#screenshots
It might be true that these all are only exceptions, however it looks very nice and improves overall ambience a lot and does not affect any game mechanism.
You are right, they never slept. You won't see it "fixed" though. As someone already mentioned it doesn't change anything game related and just adds a bit of flavor to the world. It looks more alive this way.I see that a lot of wolves and bears in Elwynn Forest are "sleeping" this is not correct at all and should be fixed =)
i'd never thought i would actually ever hear someone complain about something like this.