The Impreza 2.0i takes all kinds of measures to try and improve gas mileage and cost costs. One way to improve mileage is to program the car to tread the fine line between running ultra-lean and detonation. That's pretty "severe." Another way is to run the thinnest oil possible to reduce friction to the bare minimum. Likewise severe. Neither of these techniques is particularly kind or gentle to the engine.
It will be interesting to observe these engines after 30,000 miles, 60,000 miles and 100,000 miles, eh?
Exactly what ratio is "ultra-lean" ? 14.7:1 is normal (slightly lower for E10). In most conditions, going too lean just causes stumbling and poor fuel economy. There is some benefit in going slightly lean of 14.7:1, but not much.
Without evidence, I'm not going to assume that the 0W20 this engine was designed around is harder on it than something thicker.
It's a well balanced, small displacement engine with a massive sump, no turbo, and no towing duty.