On a thinkpad keyboard, my thumbs fall naturally on the space bar (well, rather between the space bar and the left trackpoint button), so hitting the alt next to it implies an uncomfortable bending motion of my left thumb. Also, the x is just over that key, so doing M-x in Emacs would be a weird pinch-like move. Maybe it's a matter of habit, but using CAPS as Ctrl/Esc is literally a 2mm move of the pinky to the left from my home position.