The problem with this hot/cold discussion is that there are extremes of both. In a quick search I was not able to find any stats, but I'd guess that there are more deaths in the U.S. from heat than from cold.

For me I think that in an average year in Minnesota vs an average year in Alabama I'm likely to ride to work or for errands more often in Minnesota. This past year was much colder than usual, but in a normal year there are very few and often no days when it's too cold for me to ride (and some years there may be a day or two when it's too hot/humid). In Alabama though there are likely to be several days when it's too hot/humid for me to be able to ride.