Originally Posted by OU

I'm not sure on that one really. On many of the words it doesn't really seem out of place to me, often times it makes more sense with the pronunciation to have a "z" instead of a "s". But unlike the extra U words not many z for s words pop into mind right away. Realization is one? But IMO with how it is pronounced it makes sense that way.

EDIT: after a quick google search it appears it started with Noah Webster when he compiled a dictionary he seemed to simply some words and change s to z in some words due to pronunciation.