From where I sit, Sony has always been carried by their third parties. It was a third party paradise during the PS1 and PS2 days. Sony actually launched the PS2 without a single first party game (except FantaVision--if you consider that a game) because of this. They did have the Gran Turismo franchise and, near the end of last gen, they had God of War. Aside from that, Sony has historically had a ton of franchises that were decent but often forgettable. That sorta changed this gen with Sony being forced to create some new IP's and really push older IP's but, at this point, I have to say that Sony doesn't have a single franchise that will get people to line up to buy new hardware like Microsoft has with Halo or Nintendo has with Mario, Pokemon, or Zelda.
God of War, Uncharted, Gran Turismo--all great series but I don't think any of them will "put asses in the seats" when it comes to selling the Vita. That franchise that will sell the Vita has yet to be created. Even all of the new IP's that Sony has pushed this gen aren't big enough yet. They still need to grow. Their best bet will be Battle Royal but I don't think that game is going to be huge, either--AND it's not exclusive to the Vita.
The Vita may be able to sell based on a strong library of good games but a lot of people are like me (unless you speak of the Wii) where they won't buy new hardware unless there is that one "must-have" title available to play. That initial purchase is a tough pill to swallow without that motivation.
