That might explain why there are stickers on all the Logic upgrade boxes (inside the cellophane) saying what qualifies. In the case of the ones here in Canada (whether you upgrade to Express or Studio), BigBox definitely qualifies, according to the sticker (and certainly according to those who have successfully upgraded this way).
Perhaps Apple put different stickers on the ones destined for the UK?
But the curious thing is that even the Canadian AppleStore omits BigBox from their listing: apple.ca
But the physical product itself disagrees with this.