Market research outfit Newzoo has released the highlights (PDF) of its International Gamers Survey 2010, showing that 40.1 million people in the US play games on Apple's iOS devices (iPods, iPhones and iPads). That's more than half of the 77 million mobile gaming audience in the US. Only the Nintendo DS has a larger following with 41 million gamers ages 10 and up. Both are well ahead of the PSP's 18 million.
Mind you, those aren't individual usershares or anything. There's a significant overlap between gamers of each platform. "The majority of the 160 million Americans playing computer games do so on multiple platforms depending on the time of day, social setting and mood." For instance, nearly 14 million DS and DSi users also play iPod touch games.
One interesting note is that the number of players paying for games is significantly higher for Nintendo (67%) and Sony (66%) handhelds than the iPod touch/iPhone (45%) and iPad (32%), and that's naturally attributed to App Store freebies. However, the iPad has the largest share of players paying more than $10 a month on games (72%) compared to 38% for the iPod touch/iPhone, 53% for the DS/DSi, and 59% for the PSP.