Except STI isn't a model, it's a performance division of Subaru and they make parts that go on non STI cars.

For example in Japan you could get a Forester Cross Sport SG5 with STI Genome exhaust, STI shift knob and steering wheel, STI fog light covers, STI Branded side skirts and rear bumper all as factory options, if you got the full STI package a Cross sport would even come with STI badging There's probably more I'm forgetting.

Another example is I just replaced my pitch and motor mounts with STI group N mounts which are all badged as STI, if I was driving a non STI I would still have STI branding on parts all over because they are OE performance parts and not just a model of car.