A late reply, but better late than never.
The AWD system in the VDC models is called Variable Torque Distribution (VTD).
It seems strange to me that Subaru emphasized the stability control system (VDC) when the main reason to buy a VDC model was the VTD drivetrain. But I guess Subaru chose to advertise soccer-mom safety more than performance.
VTD uses a center differential with a planetary gearset that gives a full-time rear-wheel bias. 55% rear/45% front.
Manual transmission Outbacks also have a center differential, albeit a simpler gearset with a 50%/50% front/rear power split.
The other Outbacks (i.e. most Outbacks) have "Active AWD", which has no center differential at all. Instead, they have a transfer clutch that progressively locks the front & rear drivetrains together during acceleration or slippage. You can find lots of forum arguments about the "power split" on these models...because it isn't a consistent split, and it doesn't work like a differential.
If you aren't familiar with the function of a differential, look it up on wikipedia or howstuffworks. Basically a differential allows two driveshafts (left & right or front & rear) to spin at different speeds while still transmitting all power. It is a very different beast from a transfer clutch, which locks the speed of the driveshafts.
ALL Outbacks have a front differential and a rear differential, because the wheels on each side obviously need to spin at different speeds while the car is cornering or turning.
But the only Outbacks that have a center differential are the manual transmission models, and VTD models.
The manual tranny Outbacks also have a viscous coupling that will lock front & rear together when they are spinning at very different speeds.
The VTD Subies have a transfer clutch, just like the "Active AWD" Subies, but this clutch is mostly used for wheel slippage, since the center differential already makes it a full-time AWD vehicle. So this clutch is smaller (fewer plates) than in the Active AWD model.
The VDC Subies also do not need a viscous rear LSD, because they can control wheel slippage via independent wheel braking.
In brief: If you like to drive curves, accelerating out of the apex, get a manual or a VDC/VTD Subie. They are the only ones that have a mechanical center differential.