> Every single one of these icons should be available to choose by the user.

They are. You can replace the icon of any app straight in Finder, in the Get Info window. Copy the icon from somewhere else, click the icon in Get Into to select it, and Cmd+V to paste.

I mean, you'll need to get the original icon, but that's not too much work. I don't think Apple themselves should be shipping every high-resolution icon they've ever used for every app. OS's are already large enough.