The engineer in me must point out, that the Voltage isn't the only factor here. It is Power (Watts) that matter, which is Volts times Amps.
So the UK outlets provide higher voltage, and a little lower Amps, but the Volts x Amps (Watts, Power) is significantly higher from a UK outlet. I think they ignored another factor, I'd need to look it up, but I think appliances are supposed to be limited to 80% of the outlet rating, to provide some extra margin (that may only be for 'continuous duty' things, not sure a kettle fits that description).
Quote:
In the UK, with a mains voltage of 230 V and a limit of 13 A per socket the maximum possible power to one appliance is
2990 watts (2990 joules per second). In the USA, with a mains voltage of 120 V and a limit of 15 A per outlet the maximum possible power is reduced to only
1800 watts,
A quick glance at Amazon shows US style to be 1500 watts, and UK style 2200 watts, ~ 1.5x the power. And within the 80% I mentioned. So I guess a US tea kettle would heat water in approximately 1.5 trices?
There, more than you wanted to know!
-ERD50