While Fitts' law is useful, that behaviour actually drives me mad as someone who is used to the three mouse buttons having discrete behaviours on the actual caption bar. Suddenly 'tab' is above 'window' in the hierarchy for control.
I can understand that. For me, though, I use middle click to close tabs significantly more often than I move the browser window to another monitor. So I'd rather live with having to click an empty space farther to the right of the tabs when I actually do move the window.
I could learn to use CTRL+F4 to close tabs, but I find that slower than just middle clicking the tabs.
