During the PlayStation live cast day 2 stream, Scott Rohde and Adam Boyes talked briefly about how Spider-Man on PS4 came to be. They said that Marvel actually asked Sony to create a Marvel game which would be treated as a first party title for PS4.
Marvel didn’t specifically ask for Spider-Man to be the game that Sony would publish for them. The decision to create a Spider-Man title was by Sony who then contacted Insomniac Games to develop the game. Scott Rohde when talking about how the game came to be said Insomniac Games “would be the perfect fit” due to having “next-gen tech already going”
It’s also interesting that Marvel didn’t specifically mention Spider-Man which means if all goes well, this could very well be the start of a new relationship between Marvel and Sony to make Marvel games exclusive to the PS4.