While this is not necessarily true, it's something we will only be able to verify once it actually happens, so we shouldn't worry about it until release.
The fact that they decided to do a PS4 -and PS3- release shows they believe enough of their customer base aren't getting a PS4 early enough for them to make it PS4 exclusive.
But as SoWL points out, they could focus on development for the PS3, and then port that over to the PS4.
EDIT: What evidence is there about Xrd graphics being beyond what PS3 can handle?