Its quicker in the US because of the voltage difference. In the UK kettles are quicker.
Big benefit to a kettle is not heating the container in the same way, making it easier to pour/brew. Also no timing involved as the kettle turns itself off once the water has boiled (whatever the volume) where as in the microwave you have to get the time right for whatever your bpiling.
Kettle is also great for boiling water for cooking - you can put freshly boiled water into a pot and then get it up to boiling or simmer on the hob fast.