I think you change your riding style when the temperature is below freezing.
Frost or black ice on an expansion joint/manhole cover are not to be taken lightly.
While it makes sense that cold rubber does not grip as well as warm rubber, I think the odds are better that you will find some ice.
Now, this all changes is you are pushing it in turns and accellerating hard when it is cold. I have ridden in temps as low as 7 degrees F for 2 hours on my commute. The factors that come into play first for me are:
1.) Truly dry roads.
2.) Keeping your visor clear.
3.) Rider comfort. (I don't really feel like pushing it when I am traveling at 70mph at 7 degrees F)
4.) Grip of the tires, but I find #3 to limit this.
I have found cagers to be more courteous, but I think that is because they think I am crazy. It doesn't get much colder than that where I am. Maybe some of the folks from the frozen north can weigh in....