The poll is a bit skewed. I think WWHD will outsell TPHD, but not because the NX is coming. If the NX is a home console, then it won't be coming this year, 2017 is more likely. Anyway, I've yet to see a second game in series outsell the first on a Nintendo console;
Twilight Princess outsold Skyward Sword, Metroid Prime outsold Prime 2. Mario Party sold more than MP2, which again sold more than MP3. MP4, 5, 6, 7 follow the same trend, 4 sold the most, 7 the least. Donkey Kong Country outsold 2 and 3, and 2 outsold DKC3.