That is not what we are talking about. You can scroll a screen on the amiga without moving ANY pixels at all using hardware offsets. Try scrolling a screen in BlitzPlus/BlitzBasic WITHOUT having to re-draw everything.
I though we were talking about why its hard to get smooth scrolling looking good on a PC.
Pc games work by redrawing the screen. So what? It's actually easier to code that way. And I wrote a couple of commercial Amiga (& ST) games so I've worked with both systems.
As for just having a big image, it's only "the best way" for a very limited number of games. Most games would require a bigger playfield so you'd have to do some edge updating.