What about the prove for usage of contextual menu? I'm pretty sure people use it quite regularly especially when they are browsing the web, editing text in word processor, post processing images with Photoshop or editing video in Final Cut Pro.
I for one, use it everyday to open links in a new tab. Cmd+click doesn't work on every website you know.
This is entirely my own empirical evidence (I worked tech support in a design house), but mac users seem to use keyboard shortcuts more than contextual menus. E.g. opening links in a new tab is command+click or alt+click, depending on the browser.
I've worked a lot with FCP (and other editing suites) and PS, and everyone I see, especially pros, seems to make heavy use of keyboard shortcuts and modifiers, rather than fishing around in menus.
Most Mac users don’t use Photoshop or Final Cut Pro. Most Mac users are not power users. Many don’t know about browser tabs, let alone how to open new ones with keyboard shortcuts or contextual menus. Savvy users use keyboard shortcuts to copy and paste text in a word processor, not so savvy users go to the Edit menu for every action.
(I have no proof for any of this. I have watched all kinds of people use computers for 25 years, in all kinds of settings.)
I for one, use it everyday to open links in a new tab. Cmd+click doesn't work on every website you know.