actually for the purpose of what they are doing (integrating these devices), Sony has all kinds of electronic devices, MS has Zune and 360 on hardware side where they will be implementing their store. They will never be able to implement their video/apps/games store with Windows, at least not preinstalled because they would be sued to oblivion and beyond.
So you have 50 million PSP's, 20 million of PS3's and soon to be shitload of Bravias and Phones/Walkmans that will be able to access and purchase from PSN. So yeah, they potentially have the biggest platform out there, but it is not that simple as they have started out late and playing catchup is never an easy proposition.