I understand that, but do any of the touch events fire in parallel? Like, just before the pinch happens, is there not a touch start even for when the fingers touch the screen? The idea is to change the rate of the normal scroll event only if there are fingers on the screen.

I don't think there are any touch events at all when you're using a trackpad on a mac. For mobile, we can distinguish by the touch events.

Oh, yes, I'm sorry. I completely spaced on what you were saying.

Probably for interoperability for applications that use "standard" ctrl-scroll for zoom.

It's a relatively common shortcut.