delicate porcelain teacups

Maybe that myth came from "bone china"** which is not the same as porcelain. Porcelain is pretty robust, whereas cheaper bone china uses a lot of calcium to flux the body so it almost a glass. The average person would not make the distinction. And pouring straight from the kettle onto tea bags would be a much bigger shock IMNSHO.

The exception I would possibly make is en.wikipedia.org/wiki/Lithophane which in order to make light and shade for images, it is necessarily very thin in places. I did once own a cup with a picture shining through the bottom.

** origin of the "bone" in "Rag & Bone Men"