One of Vita's most compelling features is the ability to play content that's been purchased for your PS3. For example, the upcoming MotorStorm RC will not only feature cross-platform multiplayer, but a single PSN purchase will unlock both the Vita and PS3 versions of the game.
There are other games that will offer this unique value. Hustle Kings, for example, will be free to download on the Vita if you've already purchased the PS3 version (and vice versa).
DLC purchased for the PS3 version of Ultimate Marvel vs. Capcom 3 can be used on the Vita version, and vice versa.
Finally, Wipeout 2048 will eventually feature the tracks from Wipeout HD and the Fury expansion pack. If you own the PS3 counterpart, you'll be able to download those tracks for free on the Vita. Wipeout 2048's connectivity goes one step further by allowing you to play cross-platform multiplayer across the DLC tracks.
Hopefully, more games will embrace the concept of a single purchase across multiple devices.