I always assumed it was the daytime running light issue.
In the US a car doesn't have to have daytime running lights, but in Canada we do.
The HID system has no daytime running lights. I remember seeing a chart of all the Impreza models in the US, and only the STi didn't have daytime running lights.
I thought it kept a nice theme with cheap engineering by Subaru (Sorta similar to how we only get 1 heated seat, since they took the other switch and used it for the differential control - where the WRX has two heated seats with both switches used for seats). Seams like Subaru just tries the quick fix method on some things.
Like inventing an HID system with no daytime running lights, and leaving it off the Canadian models which require daytime running lights instead of developing a daytime running light system with the HIDs. I don't think it woulda been that hard to have the little corner amber lights on all the time.
I also would've lived with having fogs that are the daytime running lights to have HIDs (I think some Audi models do this).