Probably because Subaru suffers from questionable engineering, design, and quality control? Again, I bring up the various window problems. How hard is it to engineer a proper power window a bunch of different failures, streaks, grinds, clunks, and squeaks? What about the tranny? Clutch? Seats that don't worn out in a few years? Headliners that doesn't feel like fuzz glued on plastic? My ass crack is better carpeted than that.
Toyota/Honda doesn't seem to have any problems with their North American built cars. I mean, really, it's not like American autoworkers are all fat chumps and can't torque a bolt right or insert the ECU the right way, and that Japanese autoworkers are incredible trunk monkeys that leave secret messages the side of your radio with Engrish a la NSX style and voila, your car is nearing perfection just because it's built in the land of rising sun. My mom's '92 North American built Camry had build and materials than my '02 Subaru. That says a lot, imo, considering they're priced similarly, albeit with slightly different purposes in mind.
When it comes down to it, for the most part, these cars are just assembled, and not designed here. So yes, part of the quality problem should be laid at the door of the assembler, but when Imprezas have their large share of problems, it's the QC, design/engineering that should be reviewed.
Now, don't you go mentioning GMs and Fords.