I think the Vita is doing fine and doing exactly what Sony intended it to do: occupy the space that Nintendo would eventually want to move into. Tech wise, it's a generation (if not two) ahead of the 3DS, so where would NIntendo go next? 3 screens? Smaller? Bigger? Where ever they go, the Vita is there first. Nintendo are going to have to offer better tech at some point and with better tech comes more expensive development, which is of course why less third party devs are supporting the Vita.
Because of this the Vita will be the last Sony handheld for a VERY long time.
As for the PS3 numbers ... I'm going to wait until we are into the exclusive zone and see what averages we have then. Talk of next gen has definitely effected sales of both the 360 and the PS3 though.
