Not sure how it works in the US. In Europe, we generally pay sales tax appropriate to the country of origin. In the case of the UK, this is 20%.
If the B&H price excludes NYC tax, the % difference between US and UK is or course a little lower than I said.
I was just wondering where you got that $3214 number. In the US, sales tax is a state level tax and is added onto the purchase price. B&H lists the camera for $3499. If someone walks into their store in NYC, B&H will add NYC's 8.875% tax to the item's price. If someone in Albany, NY orders it from B&H and has it shipped to them, they'll probably pay NY State's 4% tax rate but not NYC's higher rate. (At least that's how it works in California). If B&H ship the item to another state where they have no business presence, such as California where I live, no sales tax is collected. I'm supposed to report and pay California's sales tax on it but the compliance rate is about 3%.