The average person uses CAPS LOCK a lot more than those function keys at the top, or the scroll lock or pause/break key or the insert key.
I use it when typing addresses for shipping labels or sometimes the column names for excel spreadsheets or serial keys or case sensetive captchas. I know it's not much but it's still a lot more than the function keys, pause/break, insert, or scroll lock.
I've never in my life used F1-F3 and F5-F11. (alt+F4 closes windows and F12 is for full screen, those I use).
Perhaps Capslock and Backspace should be switched?