no, because people don't walk into a store going, "oh <insert multiplat title here> is coming to ps4. too bad it's also coming to xbone, or else it would've sold me on the system."
even if ps4 won't have an exclusive come fall, it'll sell units when nba 2k, cod, bf, etc. drop.
okay, let's just forget the people who bought a ps4 to play ac4 and not because of infamous. seriously, this sort of "no exclusives! no gamez!" irks me the most. people who buy multiplats are going to buy it on one system, and that one system will be the system of their multiplats for the next decade. that multiplat might as well be exclusive.