Oh I see - yes, what you're calling the multiplier is just what I calculated from Wii Sports.
What surprised me about the data was more just how many systems in the UK had data for certain games on them - now like you say, the multipliers for each game will vary from the 10 suggested by the Wii Sports data, but I don't see why such a multiplier would be dramatically lower for a game such as Z&W. True, users doesn't equate to (first-hand) sales, but it raises an interesting point: suppose an original IP is something of a commercial failure due to low first-hand sales, but Nintendo Channel data suggests that quite a large number of people ended up playing the game anyway (perhaps through second-hand sales, renting or borrowing), would a publisher consider such data when considering whether to release a sequel? I mean, Z&W may well have sold nowhere near 200,000 copies in the UK, but suppose (hypothetically) that the multiplier from Wii Sports is similar to that for Z&W. That would mean that, despite low sales, around 200,000 UK Wii owners have experienced the game. As such (given the game's critical acclaim), the number interested in a sequel might be higher than sales of the original suggested.