I've been wondering this for some time now

. Why is it that the Scion tC comes with a subwoofer from Pioneer and the xB which is a larger car does not. Larger cars need that boom. In Japan, the Toyota Corolla Rumion has a 9 speaker sound system. (8 speakers 1 subwoofer), in America our 2nd gen xBs don't even come with a subwoofer what gives?
Here's something I watched on youtube about the Corolla Rumion, it's pretty cool imo: