The largest icon size Apple requests for App Store apps, 512px square, is larger than the display of both the original iPhone, and the first Macintosh.

I believe Apple uses this large size for display promotion of the app on its store, not necessarily something it would use in the normal operation of the app.

A typical 32-bit RGBA bitmap, 512 on each side, requires four times the memory as the NeXT Megapixel display.