I have a trackpoint with no 3rd button. Many trackballs don't have scroll wheels. Many folks use arrow keys and space, shiftspace, pgup/down to navigate too and those require nice visible scroll bars that move the whole document to navigate effectively.

Long story short, stop fscking with accessibility. If your js code or libraries handles ANY input events, you'd better watch yourself because you're venturing into specialized-interface-by-and-for-assholes-land.