But wait, you may ask "How can Nintendo request the removal of an emulator if emulators are legal?" Aye, there's the rub: GBA4iOS distributed the GBA BIOS with it, which is copyrighted software and illegal to distribute. Thus was the downfall of this clever circumvention for now. Creator Riley Testut says "the site will remian offline until further notice," so it could return without the BIOS, but as a student he may not want to risk angering Nintendo's lawyers again.
Oh well, there's always jailbreaking or Android, right?