One thing I can see in your G35 example is that if you do a downshift instead of braking in that condition, all that is going to affect if the rear wheel, which is more likely to cause instability issue in bad condition. Though in an auto G35, as you noted it won't let you downshift when it doesn't get the right rpm, which probably minimize the chance of it being jerky on the downshift to upset the balance of the car....Personally in my G35 in winter(auto also) I do downshift first before I get on the brake, though to note this is in no emergency condition. As in winter anyway I usually don't try to gamble on making any corner at any significant speed....
University of Toronto Formula SAE Alumni 2003-2007
Formula Student Championship 2003, 2005, 2006
www.fsae.utoronto.ca