A few million paid copies of this game is a ton of money.
The original article stated an 8% conversion rate. At 25 million downloads and the 8% conversion, that's 2 million paid copies. At $10 a pop, that's $20,000,000 of revenue in 4-days. Nintendo and their developers get 70% of that, so that's $14 million.
All this means that it's a HUGE HIT!
Can someone who is an App developer take a guess what it would cost to get a game like this programmed and developed? Would a $5 million development budget be too much? I really have no idea.