Theres no difference i can see between the S4 part and the TDI part, bar the pre/post facelift split, although there does seem to be a difference on ONE side of the rear of cars with automatic headlight levelling, which the S4 will have.
The post facelift sensors are slightly cheaper, but none are listed anywhere near £140 on vagcat (althgouh i've no idea how uptodate the prices are on there, they've always seemed pretty close for me in the past)