Well considering that adding a battery grip makes this camera way better than the way more pricey 1Ds Mk III probably that's the reason for the high price.
Still I'd exchange it anytime for my 5D Mk II if I could, but yes it's quite pricey at the moment...who knows maybe in the future.
Way better? Not so sure about that - particularly up to iso400
Well actually the 5D Mark II has already a slightly better sensor compared to the 1Ds Mark III (quite subtle in most of the cases but still a little bit better).
Talking about functions of course the 1Ds Mk III is waaaay better than the 5D Mark II, maybe it has something more also compared to the 5D Mark III speaking of functions, but there are also lot of other functions available solely on the 5D Mark III and not on the 1Ds Mark III.
So since the new camera is about 2 stops better than the new one, it would be obviously better than the 1Ds Mark III for noise performance and picture quality, plus you get a better AF and faster burst mode.