It's also in the PS Blog that you get both.
Actually what the blog actually states is
The Pinball Arcade is out now on the PlayStation Store . PS3 and PS Vita owners take note: when you purchase the PS3 version, you get the PS Vita version bundled along with it! Running at a buttery-smooth 60 frames per second with eye-popping graphical and lighting effects, this is the perfect pinball game to grab on the go. Future DLC for the game will also be able to be purchased once and accessed on both PS3 and PS Vita.
It's probably nothing but a wording error, but since it doesn't actually say that buying the Vita version gives you the PS3 version for free, I'm playing it safe and buying the PS3 version at home rather than risking not getting the PS3 version by buying the Vita one now while at work.
And speaking of free cross-purchases : Don't forget that by owning WipEoutHD and Fury DLC, you'll be given free WipEout 2048 DLC coming "This Spring". Might be an incentive for some to pick up the bundle while on sale this week.