Threads like this make me feel good about internet forums and the fellow enthusiasts who frequent them.
I've owned a torsen based Quattro A4 for over seven years now, in a fairly snowy area. I know it has its limitations, but in my real World driving I can say that in almost 100,000 miles now (~155,000 km's so far) I've only been stuck twice. Once I was an idiot and I attempted to drive through a muddy trail with my summer tires at a MTB race. The second time I got beached on deep packed snow (with my winter tires). All other times Quattro was able to see me clear.
I spend a lot of time on M3 Post as I plan to replace my A4 with a 2011 E90, and am encouraged about the community when I read objective threads like this one.
I'd believe that xdrive may equal or exceed many forms of quattro, but that in the real World both will do what they need to for their drivers.
James