The PS3 not finding itself in so dominant a position in this round of the console wars is interesting to me. Was it because it cost too much? Because Microsoft's marketing was better? Because development was too expensive or complicated? Regardless, there are smaller, interesting targets that I think would have helped, from my biased perspective:
God of War 2 released on the PS3, not the PS2. If the same game that came out for the PS2 were instead released for the PS3 with whatever visual bang they could muster, it would have been a killer app. This might even be true with PS2-quality graphics. It may not have made development sense -- at the time I thought, Sony said they want the PS2 to last awhile, and GOW (I think) sold less than they projected, so maybe this is just a safer dev-cost bet that accomplishes this goal -- but the press around GOW2 was insane, and I don't think the PS3 found a release of that magnitude. If it had, I think the future of the PS3 might look much different now.
Little Big Planet replaced Home. Presumably after the success of Mii's, Microsoft and Sony wanted summadat, spawning Avatars and Home, the former of which seemed strong if derivative, while the latter was different for different's sake (and no other clear reason). About the same Sony decided to aim straight for the Uncanny Valley with Home, LBP was released, and I was flabbergasted by the wasted potential. If all the energy spent on Home were instead spent giving everyone, regardless of LBP ownership a Sackboy to customize and pose and share, and buying LBP still offered the games and editing tools to play with him, as well as more costume options, I think it would have been wildly more successful. Not so much a game-changer as having a killer app would be, but still a much stronger step forward. In fact, I still think Sony should do it: announce the explosion of Home, and make Sackboys a core part of the PS3 experience.