If the world doesn't have humans or the humanoids we know, then I fully expect the writer/DM/whatever to have put some serious thought into changing the culture along with it.
Me and some associates had a project going some time back about designing a world without humans, or the basic structures of a human inspired society (for more of a backwater sci-fi setting). The setting was to be used for a novel or series of novels, but the loss of the main coordinator for the group involved has left the idea on the back burner for most of us. Nothing ever got past the 'notes and brainstorms' phase, but thats still over 200 pages of notes and ideas. There was never anything that resembled a 'replacement' race for humans either, nor did there ever really seem to be a need for the developement of one. We had talked a little about porting it into an rpg context, but have done very little with it in that regard either since we never thought the idea of a total non human (and quite strange) setting would appeal to very many people. After reading this thread though, I may have to pull some of those notes back out and see where we left off at.