Exactly.
It's way too early to count up million-sellers on the Vita of course. But the point was, to provide a software kick to go along with a price cut, "that one game that does it" is the wrong approach, and probably not the one Sony would take, considering they have many studios. They can do multiple titles in different genres to complement each other, to provide a broader appeal than one single title could ever do, and to mitigate the risks of "that one game" not turning out as well as hoped.
Tearaway is significant because it gives you the full tour of the Vita's control options, along with an inclusive art style. It's an important game to have on the platform one way or another. That doesn't mean it will sell systems all by itself. It most likely won't. But then you have one need covered. Add a shooter, some character action, plus a racer or something, and you can have a measurable combined effect.