Well, if we see the numbers for Week #2 for PSV we might get the picture of how the competition between the 2 consoles will go in the near future (where nothing major changes the status quo for both parties), but looking at the 3DS's 500k+ units during Christmas week in Japan alone (which is Wk 2 for PSV) does seem to paint a worrying picture for Vita.
The reasons (about the PSV having lower launch sales) aside, I think there's another major reason why it's lower. People are afraid of the re-enactment of 3DS history.
That aside, if the whole war this gen revolves primarily around the price of each console (and that the quantity and quality of games of both consoles are on par), PSV might lose the game again (I'm pretty sure the current profit levels at this selling price might be marginal, assuming that it does exist in the first place, so price cuts after something screwed up happens won't be an option)
(Camps for Wk 2 sales numbers) Edit: Oh crap 3DS outselling Vita 7:1, plus PSP numbers are higher than its successor.