That is such a good question. In my experience, I far prefer the oily richness of a BIR curry. I have some indian friends and have asked them for their recipes and techniques an to be honest the results are never what I'm looking for.
Even if you speak to the guys who own/work in the spice shops, their recipes just aren't as self indulgent as the BIR. I can only suppose that in India, currys are dishes that you eat very often and so to use all the ingredients and go to the BIR lengths would be a real luxury. I have tried a couple of authentic recipes and the end products were pretty dry and uncomplicated.