After eating at well over a hundred curry restaurants across Canada and the US, I thought I'd post this as "typical" for anyone who travels over here and wants a curry.

I've eaten at over 400 Indian Restaurants in the US and London, and I can tell you that your experience isn't at all "typical" for the US.  Grouping the US and Canada into one lump entity is incredibly shortsighted.  Most of what passes for curry in the U.S. is a crime, but it all boils down to where you go.  You basically have areas where there are North Indian/Punjabi populations where the food is almost identical to the UK and you have areas with little to no Indian population where the food is garbage.  The most populated American area is Northern NJ, and, within Northern NJ, you have two towns that have massive Indian populations, Parsippany and Edison.  Both towns have restaurants that are almost identical to BIRs.  The differences are very subtle. BIRs will use coconut milk as an ingredient and they might add a bit more kasoori methi than their American counterparts..

New York City has Little India and Indian Restaurant Row, and those areas have very BIRish offerings, but New York also has a lot of pricier Indian places that tend to be pretentious and miss the BIR mark.

Out of around 300 places I've been to in Northern NJ, I've never had a CTM that didn't have cream in it.  Capiscum (Green Pepper) can make it's way into CTM occasionally, but no more than about 3% of the time.

Over the years, heat levels have dropped a tiny bit in the area, overall, but, there are some chefs that go heavier and some that go lighter.  If Northern NJ Indian food is slightly less hot than the UK (and, if it is, I'd probably say it only varies by percentage point or two), than that's, imo, an improvement, as the best Indian food has a sense of balance when it comes to scovilles. It should have some intensity, but it shouldn't be a sweat fest.