This is a classic case of misinterpreting the data - 85% use it because the only way you can copy, without using a context menu or a keyboard shortcut is by holding down Alt and then clicking on the Edit menu.The point is, people use keyboard shortcuts & context menus because they
have to today.
This is the danger with reading too much into simple data - just because 85% of the people do X, it doesn't mean that X is good. Do you expect the data to show that people don't copy paste because its not intuitive? No, in most cases they 'have' to learn it, and figure it out by asking a friend, but they don't enjoy the learning process (and indirectly, resent the platform itself).
Everyone who struggled with the concept of right clicking eventually learnt it - the problem is not that right clicking or context menus are impossible to learn. It's that they're not a natural way of interaction, and should be eliminated whenever possible.
You shouldn't have to learn to use a menu to do what you want, especially when 80% of the time you just need 4 actions.
The simplicity of modifiers (tap, double tap, swipe) is what makes touch platforms like iOS very intuitive. A direct, clickable button ensures that novice users can accomplish simple file management tasks by learning a single modifier (the click).