This is all very standard stuff in product design. It’s more just a surprise to UI designers because 2D design tools are very poor and don’t include superellipse as an option.
I recall this being annoying for me as an app developer trying to perfect the app icon. You upload the app icon as a square image, and Apple applies the round corners when they distribute it. I wanted to preview how it’d look on the App Store (back when every app submission would take weeks to get approved), but found the rounded corners from GIMP just didn’t match. At least they had stopped applying gloss effects by then which totally ruined the colors.