I think in a world where smartphones/tablets are prevalent, it's more natural to have the up/down motion correspond to whatever is the thing that moves on screen. For example, if the CID was tall enough to display a static list of options, and the scroll wheel moved the selection box up and down, then I would expect that scrolling up moves the selection up. However, that is not the case — the selection box remains at the centre of the screen, and the list of options moves up and down. Therefore I expect the scroll wheel to behave like a horizontal cylinder, with the list of options written on it, and scrolling it up should move the list up (resulting in the selection box moving to the one below the previously selected item).