Sony's Patrick Seybold elaborated:
"On the digital front, we are also pleased to report that inFAMOUS: Festival of Blood is the fastest selling PS3 digital game ever launched on PSN,"
We suspect that the option to pre-order the game at a cheaper price may have encouraged some extra sales. Even so, considering the PlayStation Network has been around and kicking since 2006, that's still quite an accomplishment. The stand-alone experience offers solid content for $9.99 USD, so it's definitely worth looking into.