Every manufacturer has its little quirks, some more notable than others. Honda's thing has always been efficiency, GM's is versatility, Toyota does reliability and Mazda does insanity. Subaru's approach has traditionally been clean-sheet engineering -- starting with something truly ideal that didn't need band-aid fixes later.
In the traditional sense of the term, a "four-wheel-drive" system uses a central transfer case that locks the front and rear axles together, yielding a 50-50 power split under all circumstances. This approach is fine off road, but always sending 50 percent of the power to the front wheels inevitably results in understeer -- "push" while turning -- when there's traction aplenty on the street. Subaru's milieu was never trail-only running -- it's always been rallying, which requires a system that can quickly adapt for both on and off-road performance. That's something a four-wheel-drive system, with its locking transfer case, just can't do.
A street-oriented four-wheel-drive system uses a more flexible center differential instead of a locking transfer case. The adjustable center differential allows all-wheel-drive systems to vary the power split front-to-rear to adapt to various situations. Subaru has always used a "symmetrical" AWD system. In effect, that means that the engine, transmission and center differential lay in a straight line along the center of the car, which balances the chassis and keeps all of the axle shafts the same length. Taking this idea a step further, Subaru also uses a flat-four, or horizontally opposed "boxer" engine: the boxer engine's crankshaft is right in the middle of the car, in-line with the transmission and rear driveshaft. As a side benefit, the boxer engine is also very close to the ground, which lowers the center of gravity and enhances handling even more.