Do people in North America really not know that the seasons are opposite in the southern hemisphere?

I was talking to my friend in Canada and he didn't know that when it's winter where he lives it is summer in Australia. He then told his dad and his dad didn't believe him! I remember in the Simpsons episode where they go to Australia Homer shows up to the airport with skis and Lisa tells him it's summer but I thought that was just a joke. Is this really not common knowledge up there?