If it is at all reassuring for you, my son is 3.5 and has always rear faced. He'd be particularly loud about it if anything hurt, (he was a very early talker). He's never made a peep or expressed any need/desire to turn round to forward face, even though his friends are all forward facing now. I actually thought initially that once he got to about 2 he would have complained, but he's obviously comfortable. So now I do think they just find it easier than we would to sit like that. My son's about 105cm tall now I think.
Holly, I wonder if your LO is getting sore feet (if he's like my son and says he has sore feet, he probably does, unless he's being asked "have you got sore feet" by someone all the time, in which case I find it can put ideas into their heads).... in any case, I was wondering if the angle of the seat could be adjusted to change his posture a bit? It might be worth a try.
DS - June 2010