Your argument about picking the mouse up is fair - if I lift the MX more than 3/4 of an inch off the surface, I lose any and all control. If I were consistently picking up the mouse, I'd hate the MX. It's a bit heavy to be lifting, and it's tough to hold in the air.
That said, I don't think you should ever be lifting a mouse. It's a waste of time, especially in FPS'. I remember back in the day having to lift the mouse and move it to the opposite side of the mouse pad just to get enough pad to roll to the other side of the screen.
I just tested it, and I can do a barrel roll in the USMC helo in Gulf of Oman by moving my mouse three inches from left to right. Full afterburner straight up to straight down in the F-35, took me 6.5ish inches..
If your sensitivity is high enough, you should never leave a square bigger than two hands wide and two hands tall -- do you see how that could save a lot of time, particularly in picking up the mouse?
EDIT: To give you an idea what I'm talking about..
I typically play on my desktop like this:
But if I'm lazy and want to play from my bed, I can turn the monitor and put my mouse like this -- I just played two rounds on oilfields and didnt have to move the mouse outside that little area the entire game..