Hmm, good question nrv (and welcome to the forums). The standard setting for the mouse scroll wheel is in the control panel-hardware and sound-devices and printers-mouse settings (or just search the control panel for mouse). Try setting the wheel option down to 1 line/ 1 notch to scroll. That should smooth out the mouse making the screens jump too much while in a Metro app.
In the meantime, I have noticed that even on this lowest setting my Logitech G9 wired mouse has a tendency in Win8 to jump too far in scrolling through my Directory Opus folder listings even on its lowest setting. This never happened on Win7 which was very smooth even on 3 lines per notch.