[inverba]

A lot of teas need the water to be a specific temperature before they are put into cups/have the tea leaves inserted. Even if "the water ends up in the same uninsulated cup", the process of getting the water to the correct temperature will be more efficient in an insulated container.

Also, it's hard to believe that this would substantially decrease the amount of water heated. If you were super anal about only heating the water needed, then that's do-able with a tea kettle. If you're not, then even under the new model you would probably just use a kettle or pot most of the time.