Most people buy multiple controllers for their game systems. That's more of an anecdotal or common-sense conclusion than one based on statistics, but we think it holds. Even people who live alone generally like to have a second controller around for company. And with the Wii's status as a party system, a lot of people are likely to have third and fourth controllers as well.
Nintendo found a way to get many of these controller sales to count as software in NPD: by bundling controllers with a game and adding just $10 to the price. And the strategy has worked. Nintendo told Gamasutra that since the product's launch in February of last year, 7.9 million copies of Wii Play have been sold in the US. That's more than half the number of Wii systems sold in the US (15.4 million).