I'm going to go to bat for our American friends and say that there's nothing wrong with boiling water in a microwave if that's the quickest water-boiling-method you've got. Boiling water is boiling water, who cares.
America's greater sin against tea drinking is their habit of letting the water cool down and then steeping a bag in the barely-hot water so that it makes a drink the colour of dehydrated urine. Why drink tea if you don't want to actually taste the tea?
But then on the other hand iced tea is nice, so they do redeem themselves a little.