I know that you can't use "logic" to solve some problems, Politics and Religion spring to mind but just think of it this way ........

When God made Heaven and Earth, did He rest on the first day and then work for the next 6 or did He work for 6 days and then rest on the 7th? So then if Sunday was God's day of rest, surely that day would come at the end of the working week.

I guess that only works if you believe in God.