Earlier quoted context omitted.
Interesting. I've never seen Fitt's law invoked to cover close buttons before. Note that serious users (who are the ones complaining the hardest about gnome-shell) never touch the close button: closing a window is a keyboard shortcut (generally Ctrl-w, though sometimes Alt-F4 if the app doesn't handle that) in my world. For a while I was running a custom metacity theme with no window controls or title bar at all, act…
The point is that those corners are some of the most important screen real estate, taken advantage by other DEs. Take Windows, for example. Upper-right=close, upper-left=context menu, bottom-left=start menu, bottom-right=show desktop. Compare to Gnome Shell: Upper-right=settings/account menu (rarely used IMHO), upper-left=activities, bottom-right=missed notifications, bottom-left=nothing. Where Windows puts something…
Now, tell me, under Windows, how many times a day do you use a window's context menu, against, for example, the Start Menu? How many times do you expect a regular user to click on them? Furthermore, how many times can you activate a context menu from that position? Do you always use your windows maximized? You shouldn't optimize the corners of your screen for a windows button (because there might not be a window there). INSERT: the corners in gnome-shell always work the same way, independently of any window state.
Having something in every corner of the screen doesn't mean that it is universally useful.