The logic makes some sense, but if it were followed, new systems would never be released because the older ones have a larger userbase. I know the Wii Motion Plus isn't a new system... but it is like the DSi, which has exclusive games on it not available to the tens of millions of DS owners.
Also, one point, as I said, there are hundreds of minigame collections on Wii, including Mario Party 8 which is still selling. What does this game offer that none of the others do? Maybe it'll use it, but not require it, but even then, the games wouldn't be as intricate if they could be played with a regular Wiimote. And I really think that, if this game were going to use it, it'd have been announced with this reveal.
We know there are 16.4 millions Wii Motion Plus out there because Wii Sports Resort includes it and that's how many copies it sold. Then add in the millions sold with Wiimotes and other Wii Motion Plus games, and it has to be at least 20 million. Then figure that Zelda is being released before this and will include Wii Motion Plus, and that's even more in consumers hands by the time this game released. There will probably be 30-40 million out there at the time, at least.