Who knows? They might end up pricing the PS3 version at 50, or even 40 dollars. I doubt it though.
But yeh if it is the exact same game that is going to be kind of weird. PS3 will probably have sharper graphics though and of course much easier local multi.
Sony and Microsoft intentionally set specific price-points at which almost all games are released on their consoles. They do this to create an illusion of arbitrary value to the system itself, which is higher than what the Publishers actually think the games themselves are worth.
Example: LEGO Batman 2
PS3 = $50 Vita = $40 PC = $30
A 20 dollar price-difference for the exact same game between the PS3 and PC versions.
Even more extreme examples are "Transformers: The Movie" game and "Monster Madness: Battle for Suburbia", which both released on the PS3/360 for $60.