Why would you make a Vita only game now? To flip this argument around, let's pretend that instead of the Playstation Vita, Sony had made the Playstation 3 Portable and launched that in 2011. Would you suddenly say there's no reason to make PS3 games anymore? That's why I find this whole angle preposterous. The only thing that's going to kill Vita exclusive games is lack of Vita adoption in-and-of itself, and this is one way to hopefully alleviate that issue.
As for touchscreen support, as I said before, I wouldn't discount that completely. And as someone else
pointed out, there's apparently already some level of touch support for DS3 controllers, so there might be stronger potential for touch support to begin with than it might first seem. And even then, I'd still wait until next year when PS4s are launched and DS4s are out in the wild world-wide to see if there's a stronger possibility for proper touch support after DS4 becomes the default controller. But this is admittedly total speculation on my part.