>> Why is this hard for otherwise intelligent people to grasp?
Computer scientist Edsgar Dijkstra was quite intelligent. He argued vociferously for numbering things beginning at zero.
http://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html
Besides, we couldn’t wait until 2001 to have the “why two kay” crisis. “Why two thousand and one” crisis just wouldn’t have had the same marketing appeal. :-)
Good thing this guy is not in control of counting. In programming, yes, it is convenient to have an array that has an index of 0. That helps during calculations. But it is better conceptually to have indices begin at 1.