There is one place in America where the PSP has maintained a clear popularity over the DS over the past year: the New York City subways that I ride.
Look over to the right of this blog and you'll see the Stock Report, a tabulation of some of some bits of info, including a count of every handheld gaming system I saw on the subway in the past year. That's right: I didn't see a single Tapwave Zodiac. And I saw almost three PSPs for every two DSes.
The official MTV Multiplayer count is: 67 PSPs, 44 DSes, and 6 GBAs witnessed by me between 6/15/07 and 6/15/08.
What's this mean?
The PSPs' subway success appears to contradict sales trends. The DS consistently outsells the PSP according to NPD sales numbers. In May, for example, the sales-tracking group reported that the DS sold over 452,000 units in the U.S., compared to 182,000 PSPs. But on the number 2 and 3 trains and on the C line I see the PSP trounce the DS.
I highly doubt I know anything that NPD doesn't. Instead, my best guess is that the conditions of the NYC subway are ideal for PSP playing. On the subway people from all levels of society, with all measures of disposable income stuff themselves in for 30-minute, $2 rides. Many riders have the time and the money to play PSP. And the people least likely to ride the subway when I'm on it are one of the DS' main audiences, younger gamers who are still in school.
Back when the PSP was announced, it struck many gamers as the kind of machine they'd like to graduate to after playing the Game Boy line in their youth. But, from what I can tell, the New York City subway is one of the few venues where adults have the means to play PSP. And, by the way, they are playing the PSP on the subway. I look over people's shoulders (nosy reporter's prerogative!) and I see people playing disc-based games, not pirated emulations of old stuff, and certainly not bootleg movies or homebrew hacks.
Sony, if the whole world was the C Train, your handheld would destroy. (But given the quality of the C Train, I might have to find a new planet.)