as the title says, I’m curious to know if there’s any reason why AirPods purchased in the US couldn’t be used with an iPhone purchased in the UK. Obviously the charging adapter would be different but in terms of the AirPod hardware?
Nope, 2 (territorial) SKUs are available - MV7N2ZM/A and MV7N2AM/A. But indeed, they are completely compatible with all iPhones. Doesn't matter where you purchase the AirPods from.