Do you have proof that PS4 is rendering CoD at 720p?
A few sources don't actually show a resolution difference.
In spite of the IGN comparison saying they clealry see more detail and PS4 is higher res, the actual video seems to show both consoles at the same res.
http://i.imgur.com/Ey3teLD.jpg
And more:
http://forum.beyond3d.com/showpost.php?p=1805244&postcount=3791