I think that's the key, long before Canadian use. Interac Direct Payment (1994) has a 16-year head start on Visa Debit here (2010). I think many Canadians think of debit and credit cards as two different beasts because of the history.
I recall when I lived in Australia for awhile that I initially found it odd when I presented a Visa card and they asked "credit or EFTPOS?".