I have found that on snow covered roads, a day or two after it has snowed (when traction is the worst) a skinnier tire seems to track better. I won't say that it has more grip or bite on the road, since I don't think that's true, but I do think that being narrower allows the tire to be affected less by the grooves and variations that form in the packed snow/ice. Plus, once the streets clear, you've got less rotating mass for all your regular driving, which helps in the gas mileage and acceleration departments.
Think of driving on ice as if you were driving on water. The friction of the tire on the ice melts a very thin layer on top and causes the tire to 'float' or hydroplane just like driving over a puddle. You are right of coarse about the whole coefficient of friction idea. This is why wide has less friction on ice then a more narrow tire. Ever driven a empty dually pickup on wet roads?. At least that is how I understand it. All science aside, from personal experience, I have driven on both wide and narrow tires and I will always stick with a narrow one for the ice. Since snow does not behave as ice does a wide tire will provide both more traction as well a more flotation.
This is the Dunlop Radial Rover R/T which is a super aggressive studdable tire. I was going to switch to 16" wheels and run these in 235r85 which are about 32". Then I found the BFG's 33x9.50 which fit stock 6" wide wheels. Most tire places will sipe them for $10 each.
One downside being that siping instantly voids the warrenty which many people seem to need when running BFGs. It helps for sure but is still a band aid fix on a poor tire choice in my opinion unless you see minimal road use.
