Surely it's 's' not 'z'

In Ireland and England the convention in the written word is that 's' is used in preference to 'z'. Newspapers, journals and most books write 'organisation' and not 'organization'.

Yet it seems most 'church' 'clerical' written material goes for the 'z'.

What at all is it about 'religious' material that seems to have that amazing tendency to alienate the reader?