The PSP had stronger than expected sales over the holiday season, but in New Zealand it's the number one portable. Kotaku is reporting that in November and December of last year the PSP got 73 percent of the handheld market with 9,560 units sold.
Just to make sure that Sony wasn't giving away free monkeys with the PSP in I checked out the Sony site for that country. The only monkeys I found were from Ape Escape; other than that, it seemed like an ordinary PlayStation site to me. So it seems the game releases and the functionality alone sold the PSP. I can certainly understand why--it worked for me. Maybe I lived in New Zealand in a past life.
[Update 1: Added crucial piece of info: the country where it's PSP FTW! Also, fixed a few formatting errors.]