The problem is;  neither the DS nor the PSP has any killer apps, at the moment, that will make EVERYONE go out and buy one.  However, the DS has two looming on the horizon;   Pokemon and   JSS, while the PSP has none.   Sony needs to capitalize on the downtime before  Pokemon and JSS to  get a lead going  on  Nintendo, and try to  ride through the storm of those two games.  Which is what I think they're trying to do, hitting with some big titles forthe PSP in december, such as Metal Gear Acid and   Ridge Racers.   However,  they need something to counter   JSS and Pokemon.     
It'll still do very well, however.  And perhaps the PSP won't even need a killer app to sell.