Maybe its just because of history Pete.
With the E9X range the 335i was ALWAYS compared to the 335d and NOT the 330d. Maybe old habits die hard so people still
are not comparing the 330d to the 335i.
Also in the past the 330d was compared to the 330i - now the 330i is replaced by the 328i. Its just the 330d has moved on with performance and the 330i/328i hasn't (no point really as we have a 335i!).
The 330d is more closely matched bhp-wise to the 328i (245 vs 258) only 13 bhp difference whereas the 335i is like 50 bhp more. Although I realise the 330d has a shed load more torque than both.
Price-wise the 330d is around £2K more when you put the same 'box on the 328i, so not a vast amount more in cost. The 335i is about £3K more than the 330d with the same 'box.