You know, I'm not sure why I didn't try just mousewheel. On 7.0.7.26 I get the same behavior as you do, mousewheel to zoom, and ctrl-mousewheel to scroll vertical. I do not seem to have an interface to customize keyboard shortcuts outside of the arrow keys, page up and page down, and space and backspace. Maybe I'm missing something.
It seems that the official documentation is either out of date or incorrect then, yes? How would we go about requesting that be updated?