Hot weather and cold weather commuting are different beasts and it's hard to compare them. I really don't mind the sweat, -unless it gets into my eyes.
While I can dress to be more or less comfortable on most winter days, there's a lot more hassle. Studded tires and poor road conditions slow you down. Plus it's dark most of the time.
By more or less comfortable I mean that my head could be sweating while my toes are numb, but that averages out to A-OK.
On the other hand, in the winter I really don't worry about over exerting myself and my water is always ice cold. In extremely hot weather, having enough water and not pushing too hard become a much bigger deal. It's not really a problem for my commute so much but becomes an issue on longer recreational rides.