"The average person would not make the distinction."

OK, I own up: I am an average person, as far as porcelain is concerned.

And I think you are right about boiling water poured straight from a kettle onto a teabag. But the same goes for tea leaves (or teabags) in a teapot. I have sometimes found cracks developing in teapots, but metal teapots, even silver ones, are not as comforting.