US electric stoves are wired into higher power circuits. The stove built-in to the kitchen is just as powerful, though there are transmission losses heating the kettle.

Countertop kettles use less power here because of the plugs, and it takes about the same time as a resistive stove.

Gas stoves here have nozzles that shoot the flame from the center away from the pot you're trying to heat. You have to choose between slow heating from a tiny flame, or slow heating from heating the air next to the kettle and the handle instead of the kettle itself.