No, it's as you say, it's just RWD and e 18d engine which is the lower bhp version of the 20d. All else is the same. I just ordered one here in the uk, and they now come with DAB and Bluetooth as standard too. I read a couple of reviews online saying at with good winter tyres you're no worse off in bad weather without AWD, especially if you're in fairly temperate land like the Uk has. And the motorway performance is very similar to the 20d but with the advantage of being about £2500 cheaper and lower running costs.
Funnily enough, a friend just sent me this link, in which the prospect of a RWD X3 is lauded - before the sdrive was launched: