I think there is no real difference. Its just that the developers wanted to make the games look better on ps 4.
PS4 is more powerful than the PS3 based on their architecture, we can clearly see the difference in their graphics ability. Another difference is that PS3 can play music CDs, while PS4 can't.
lol, this would be like going back in time a little bit and saying, "ya man, my car has a CD player AND a cassette player ?Wow, the PS4 is six years old and I never knew this (I even Googled it to confirm!).. ?