That said, I don't think people are getting iPads in lieu of 3DS or Vita systems. There's not much evidence sales wise to indicate that the market for dedicated gaming systems is shrinking.
Interestingly enough, DS sales actually GREW overall right up until the release of the 3DS From there standard platform transition shenanigans combined with some misfiring on Nintendo's part resulted in a down 2011, which was then subsequently blamed completely on the Rise of Smartphones(TM) for no good reason.
I am curious to see how the Vita does though. The annoying part is that if the Vita fails to establish itself as more than a niche product no one will ever acknowledge it as having failed on its own merits because then they can just conveniently blame Apple again, regardless of the actual circumstances.