SafeSearch vs Mature Content Filter

[Umbra]

Anyone know/guess why Yahoo.com has "SafeSearch" and Yahoo.ca has "Mature Content Filter"?

And why is SafeSearch OFF by default, whereas the Mature Content Filter is ON by default -- I can't imagine that Canada is more conservative than the USA.

I assumed Yahoo was running a temporary test, except that the discrepancy seems to be around for at least a year.