It is unclear where this data comes from, but I am guessing it only includes publically accessible BitTorrent trackers and peer-to-peer networks. In reality, the numbers are likely higher.

Across both platforms, the titles most downloaded are "hardcore" games or games that appeal to everyone. Partial lists of the most downloaded games can be found at Siliconera for both the DS and PSP.

CESA does provide an estimate for lost revenue based on the illegal downloads, but converts 1:1, assuming that every download represents a lost sale.

Sony recently attempted to fight piracy with the PSPgo, which largely flopped. Nintendo has been vigilant in going after companies manufacturing or selling hardware needed to play illegal DS games. Expect Nintendo's 3DS and Sony's rumored PSP2 to ramp up the copy-protection.