I don't think there's any physical difference between water boiled in a microwave vs in a pot (free radicals?).

Lighter teas (white, green, chamomile, etc) are best brewed at 70-80C, so that's not general advice :)

There isn't any difference, except often when people microwave water they don't get it all the way to boiling. With a kettle it's pretty obvious when your water is at boiling.