Entirely believable.
Right now, the Wii is at 35,428,210 in the Americas. If it sells as many in the next 12 months as it did in the last 12 months, it will hit 45 million pretty much right at the start of November 2011. And that would place them at pretty much the optimal point to discuss Wii 2 if it were to be released in Holidays 2012.
Of course, he said in the US, in which case it'll take a little longer - but based on Holiday performance of the Wii, it could definitely achieve that by the end of 2011, especially if Skyward Sword has a strong impact on sales, or Nintendo has some massive title up their sleeve.
As I can't see Nintendo launching their system before 2013, anyway, I'd say that Reggie's pretty spot-on in his statement, and Nintendo won't start talking about a successor to the Wii until it hits about 45 million in the US.
