Basically, an AWD car has three differentials-- the two on the front and rear axles and the one in the center* that decides how much power to send to each axle. The drawback of this is that, just like a regular differential, the center diff can be “fooled” into sending power the wrong direction in slippery conditions. Subarus are the only lower-end AWD car in which all three power distribution points are limited slip units that are harder to fool. This means that short of high-centering or having literally zero traction on all four wheels, nothing will stop a Subie. On a regular AWD system with open differentials, if the traction difference is bad enough you can get stuck with just one wheel slipping. Some are even worse than that (like the older CRV’s) in that the power distribution is all or almost all to the front until the wheels actually start slipping, which is even less useful because you ideally want to avoid breaking traction in the first place.
There’s drawbacks to the Subie AWD system, which is why the other cheaper cars don’t have similar systems. It’s very choosy about tires and driving around with unevenly worn tires can cause serious damage. It’s also partly responsible for Subarus’ relatively poor gas mileage for cars their size. But for the money they are by far the best on-road snow vehicle you can buy, which is why they are so ubiquitous in some parts of the country.
Traction control does go a long way to helping crappy AWD systems not suck so bad. And more vehicles have been coming with the center diff locks, which makes it so the center diff sends a fixed amount of power front-to-back much like a part time 4wd, which means that at least both axles are getting power which can help, or at least make it so you’ve got two wheels spinning on the ice instead of one!
*or a differential-like power split device