I don't think Vita sales are that much of a surprise. Right now it has less compelling games than PSP (or 3DS in particular) particularly for Japan I think.
Yes it's new, but its still sharing shelf space with a sibling with legs in it locally plus a now decently established 3DS with some key titles just released.
The Vita was never going to come out doing gangbusters in Japan in IMHO. It'll grow if they give it the right titles and move it into pole position ahead of the PSP for all new software.
People really expect too much from new hardware launches IMHO. Sony, Microsoft and Nintendo would have ditched most of their systems if they reacted the same way after a few weeks sales. So far Vita has launched better than PSP so far as I know which means it's positive in relation to where PSP started and if properly managed in the market can grow from there.
Try to be reasonable... its easier than you think...
