Apple loves to have a simple, black and white line art icon for products that allow you to instantly know it's an Apple product. Think original Mac/Plus/SE/Classic look, think iPod with screen and touchwheel, think classic iPhone screen + home button visual. These have broad-based recognition amongst the general public, at least if you were alive during the time. This kind of recognition is what is referred to as 'iconic.' Some other examples of iconic - the Nike Swoosh, the Coca-Cola word mark, the old Absolute vodka advertisements, and of course, the Apple logo itself - words really aren't necessary to convey the meaning (the Coca-Cola logo is recognized even if you don't necessarily read English). When you see one of these iconic marks, it's not just the name, you also cue up emotions and memories - quite a lot that's conveyed via something so simple (especially the Swoosh or the icon of the iPod).

With the move to full-screen iPhones, the line art would be a rounded rectangle on a rounded rectangle, which could be Samsung, LG, One+, etc. Adding the notch makes the design visually distinctive. It's form following function, but done in an elegant way (check out the bezier curves of the corners of the display and the notch - clearly time was spent refining them to make it as elegant as possible). I don't even notice the notch when using my iPhone, but I do notice it when seeing an iPhone from a distance - it's a clue in that you're seeing an iPhone. I don't expect the notch to go away for at least 3-4 more years - and when it does, it will be for a major change in the visual language of the devices.