The reason these don't have scrollers is that the whole idea of e-paper is that it uses no power when displaying something, only when changing it. the page turn interface capitalizes on that and makes it much more efficient than constantly scrolling. It seems that scolling would use a lot more processing power as well, whereas the page turns would just be quick processor tasks.

Also, it makes it feel much mole like a book than scolling, but I think the real thing is the battery life.