macosmousezoom
I am using a Magic Mouse on Lion and I have scroll direction set to natural.
I find the inconsistency annoying.
Thus, I'm wondering whether Apple has an official usability rule regarding what direction constitutes the recommended scroll direction for zoom in?
You can change this in "System Preferences" -> "Mouse"
This change actually happened from Snow Leopard to Lion with the introduction of Natural Scrolling to match iOS scrolling behavior where the motion is expected to work on the content - not the scroll indicator - as the two move in opposite directions.
There's no direct equivalent in OS X - the closest is probably to simply decrease the resolution.
TinkerTool has options to change system and application font defaults, but doing so may cause application or OS crashes.
Best Answer
If natural scrolling is disabled, scrolling up zooms in in all of those three cases. Scrolling up zooms in the screen even if natural scrolling is enabled though.
Scrolling while holding control could be considered to be a separate gesture where enabling natural scrolling does not invert the scrolling direction. When using a multi-touch surface, I think it's more natural that dragging up increases the zoom level.
It's also possible that applications shouldn't invert the scrolling direction when scrolling is used for zooming, but many applications do. But I didn't find anything about it in the HIG, and I don't know any applications by Apple where scrolling while holding option or command would have a special meaning.