>>“Whilst, for example, US operators insist upon qualifying their First Officers to a lower standard than their commanders, I accept that their SOPs might best reflect this. <<
Well, I've flown with Brits and Americans and have a couple of expat British style ATPL's and a U.S. ATP.
Americans are far less concerned about ego and standing on ceremony in the air, some of this is cultural, a lot of it is from recent CRM philosophy.
Brits are obsessed with detail stuff like R/T procedures (you can see the endless stream of threads on the subject here). Americans figure that if you say it loud enough and long enough, they'll eventually get the message. We can't call out flight levels below 180 correctly for love or money. We're more concerned about how much time off we have and how much money we make. Our respective pay rates and R/T procedures continue to reflect these differences in emphasis.
Procedurally, we Americans like to keep things as simple and foolproof as possible. In the British system, the more extra callouts (like every 5000 feet of altitude) and busy work involved, the better the SOP's. Similar differences are found in the licensing systems (and fee structures).
In the British system, a high checkride failure rate means the standards are high, in the U.S. system it means the training is lousy.
I'm told the British love of procedural complexity in aviation comes from the sailing days when things were made intentionally difficult so the enlisted men couldn't mutiny and run the ship themselves.