Americas/Japan is actually really misleading when looking at Zelda sales, because.... well I made a thread about this, hold on
http://gamrconnect.vgchartz.com/post.php?id=3625212
You don't have to click that, I'll explain the point here.
Zelda is actually growing steadily in America. Twilight Princess sold more in America than Ocarina, which did more than LoZ. EMEAA has seen much, much faster growth. The reason that the series seems stagnant overall is because it's been losing more and more appeal in Japan! Japan is the only problem region for console Zelda, whereas it's continued to grow in the West - individually and together.