Many games on console cap the framerate at 30. So it's quite possible we'll still see that this gen. The easiest things developers could do would be better anti aliasing on PS4, or general post processing effects. You're not going to see night and day differences, but Digital Foundry comparisons should always come out in favor of the PS4, or the developer just didn't give a shit.
Minimum frames per second are just as important. If a game constantly dips below 30 on XBone and stays steady on PS4 the exeperience on PS4 is a whole lot better. This matters. See: multiplat games that continue to sell better on 360 because the PS3 version used to or still suffer from worse framerate.