El Brezko makes me sound Croatian.
Seriously though, do you have an explanation for it? Your theory on the dropping of the U atleast holds some (water) weight, but there's no conceivable reason as to why you would replace 's' with 'z' on so many words.
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.