The more I think about it, the more I think Sony honestly doesn't care how the Vita sells this year. That when they say its sales are "acceptable," they mean it. The Vita is a long-term investment for them. How it sells right out the gate isn't important in the long run. What matters is that the console is on shelves, slowly but steadily building an install base. As production and development costs slowly drop and software sales slowly increase, the Vita will eventually become a steady stream of income for Sony -- probably not this year, maybe not even next year, but soon, and for the rest of its life.
Basically the same strategy they employed with the PS3. It started slow, but it's doing just fine now. Sony isn't looking to dominate the dedicated handheld market; they really aren't competing with Nintendo... at least not yet. They just aim to make a product that will be profitable for them, especially in the PS4's early years when it will likely be a money sink. They want the Vita to counter-balance those losses. Hopefully Vita sales start to pick up next year and this strategy pays off for them.
Think of it like a sports team that isn't even in the running for the playoffs this year giving a huge multi-year contract to a superstar, hoping he/she will help them be contenders next year. They don't care how the player does this year, only in the following years when it counts.
