The last couple of pages of this posts have really stimulated debate!
I can empathise with many of these points of view. I'm not 'blowing my own trumpet, but I think my curries are better than most of the ones available from BIRs local to me, most these days seem to be absolute crap! BUT, and it's a very big BUT, I cannot get close to the best BIRs I've ever had....
I know exactly what everyone is saying when they mention an aroma and savoryness that they cannot seem to replicate! And it is true that there seemed to be more BIRs about in the 'old days'that could pull it off! So many BIRs now use 'short-cuts', such adding tomato soup, to achieve a sometimes passable, but never fantastic, flavour!
I too, have wondered if some now outlawed seaoning was used formally, before maybe EU regs prohibited it?
Back in the early 80s (yes, I really am that old!), I used to go to a really cheap place in Leeds called the 'Islamabad', all the curries tasted similar, whether I ordered a madras, korma or something called a 'masala' (not tikka masala). BUT the aroma and taste was fantastic. I WISH I could replicate it, even though I can make a better madras than my local take-aways!
The search is fun, but infuriating!