So can't people who want to offer an in-app "tip the developer" feature simply comply (without paying Apple's commission) by selling a token physical good such as a button, sticker, t-shirt, or other merchandise?
It sounds like that should be allowed. But I think that fulfilling button, stickers and t-shirts orders is pretty expensive, and only makes sense if people give big tips (eg. if someone tips 5€, there's not going to be much left after you pay someone to mail them a sticker).