My hunch is that the pickguard is altered on PJ basses so it surrounds the split-P pickup more elegantly, and this would give the illusion of the J pup being farther from the bridge.
Or maybe it's just that treble coil on the P pickup causing the illusion.
You may be onto something.
In fact, I think maybe the whole control plate is pushed back farther to accomodate the PG. My eyes were looking at how the PU was much closer to the control plate and thus, I thought it was closer. But it may be that the control is what is not in the same place.