I don't think someone would do a perfect port of a game to the Vita just because they made an awesome job making ports of PS2 games because the PS2 is an inferior console to the PS3, it shouldn't be that hard to port a game from the PS2 to the PS3, the Vita on the other hand has the disadvantage of being an hand-held, making it much harder to port a PS3 game to it.
Lets go back and have a look.
The PS1 was not very powerful and pretty easy to make games for. Then the PS2 came along and it was an extremely powerful device, but a nightmare to work on. Developers had a very hard time making for it, so obviously everything that came out had a considerable amount of effort put into it. But the PS3 was even worse. Sony made the PS3 be a PS2 all over again. Way powerful and very challenging to make games for. They are both very different types of hardware.
By the time the PS Vita was being planned i'm sure Sony noticed how well indie smartphone games were doing, and they realized that gaming consoles need power, but they especially need developers. So I think the Vita was kind of leaning in that direction. I do believe (I could be wrong though) they created the Vita as this powerful handheld (as usual) but made it a little less difficult to make games for than the PS3. I also believe that they tried to make it capable of almost running PS3 standard games.
This would explain the wonderful Rayman: Origins, Metal Gear Solid, and Sly Cooper ports. But of course our favourite heroes Ratchet & Clank have been having a bad porting experience.
The problem I think, is that Insomniac have a tendency to get every drip of power out of a device. The PS2 trilogy was all over the place. For example: The assets which needed to load faster were kept at the center of the disc so they would load. This little 'feature' made the port a nightmare to do. The same problems would likely appear in a PS3 to Vita port too. Insomniacs tricks have caught up with them, and if they want their games to be easier to port they would probably need to change the way they make their games.
A port is making a game run on different hardawre. There are two factors though: The game, and the hardware. Lots of people forget about the game and see that if Rayman: Origins went from PS3 to Vita well that Qforce would too. But they are different games.