My other car is actually a Toyota Urban Cruiser AWD which I used to get about in the snow last winter.
In the middle of the ice and snow this time around, I actually chose to go out in the Lexus. Overall it's safer. The 4WD gets going OK, after a bit of diff-locking etc. but it's cornering and stopping abilities just can't compare to the Lexus on the winter tyres...even though it's 4WD.
Some more interesting info from Evo mag, here -> http://www.evo.co.uk/news/evonews/248524/winter_tyres_tested.html?CMP=NLC-Newsletters&uid=21c509ebe0c2b48d0fa5eb1823fd5580