I'm not sure about the non-Imprezas, but the Impreza and WRX since MY 2000 (the bug eye models) use 3 visciously coupled differentials to distribute power. The central diff is a planeviscously coupled unit controlled hydraulic electronic instruments and distributes between the front and rear axles and one between the each wheel on each axle. The autos have a hydraulic clutch planetary gear type differential. The STi trades out the central differential for an electro-magnetically controlled mechanically coupled DCCD (driver controlled central differential) to distribute power forward and backwards.
If one wheel loses traction its lack of resistance to torque will case it to spin just like an open differential but upon feeling the lack of torque delivery, the center viscous unit will send as much torque as it can to the other axle (up to 65% aft or 35% fore). As long as both of those wheels have traction, you can usually drive. Now, the DCCD in the STi's is really trick because you can lock the axles together and do a 50:50 split. I have dug myself into some 2+ foot snow and managed to rock myself out with the DCCD locked. It drives like shit on clear pavement around turns though like this.
Anyway, if the other Subbie models are like this than some snow tires and common sense and you should be able to get out of just about any situation provided you didn't jackass your way into some real bad shit, shit which you be stuck in no matter what you drive, unless you have something like a Wrangler Rubicon with a winch.
Last edited by CheeseForSteeze; 09-21-2011 at 06:30 PM.