I'm pretty sure that that was just a Superstore promotion, with everyone else responding to the competition. If I recall correctly, Cubes in any Canadian Wal-Mart (which is competition-proof when it wants to be) I went into were holidng right at $120, and never dropped then bounced upward again.
Of course, this is based on hazy memory...I wasn't exactly shopping for a Gamecube at the time.