Those who analogize the PSPgo, with its library of Minis titles, to the iPhone should remember that developing for both is not just about code. It's also about the costs every Minis game must pay for an ESRB rating.
Sergei Gourski, developer of the iTunes App Store hit Fieldrunners, said PSP development is "definitely more serious business and not for casual non-developers." Not only is investment in a dev kit "a must," you must also set aside money for "getting ratings for your game.
"The costs of ratings such us ESRB is significantly more then we had realized."
Fieldrunners, notes Gamasutra, is $2.99 on the App Store where no rating is mandatory. It's $6,99 on the PlayStation Store, where its ESRB mark is pending. As Joystiq notes, such ratings can run $2,500.
That said, Richard Stenson of Solus Games still sees PSP Minis development more for its opportunities than its drawbacks. He's put out five titles for the App Store and ported one to the PSPgo. "All I know is five to seven years ago the idea of publishing a game I produced completely myself on two multi-million selling platforms and one of them carrying the name 'PlayStation' was only a pipe dream," Solus told Gamasutra.
Update: The ESRB's Eliot Mizrachi contacted Kotaku to correct the record regarding ESRB ratings and their cost for smaller games.
ESRB ratings are voluntary; there is no formal requirement instituted by ESRB that games carry our ratings. [Kotaku] also cited Joystiq which cited an incorrect forum post that states that game rating costs are $2,500. ESRB has a reduced fee of $800 for games that have development costs under $250,000, which would likely apply to virtually all PSP Minis.
Devs Size Up PSP Minis Development Vs. App Store Games [Gamsutra via VG247]