is reminds me of something........I made a Tarka Dal a few months ago and played around with the last bit where you add fried spices. I basically decided to use loads of fresh garlic, some onion and a couple of spices (small quantity) and my old favorite - ketchup. It had the taste. I'll dig out the recipe if anyone's interested.
The point is maybe the fried onion/garlic is a major factor. It kinda links to other posts about adding precooked onions. I've never bothered to try for curries before but this is starting to sound promising.
One other point when I made this recipe was when the ketchup hit the fried mixture, the 'smell/taste' hit my nostrils immediately. It was one of those 'FFS stunned moments'. The same feeling I got the first time I played Super Mario on an N64 and realised the 3D intro was the same as the game - you know the feeling - big smile, jaw drop moment

Anyway, please don't underestimate the ketchup - I got this tip from a Glasgow Restaurant owner a few years ago. I did try to pin him down on exact quantities and procedure but he was very scant on detail. He also said they used a good 'vegetable curry powder' - never figured out what that was, but he did say you could use any kind. That seems consistent with other reports on here.