Infinity Ward's executive producer Mark Rubin briefly explained last week why there was a disparity in the resolution of Call of Duty: Ghosts on Xbox One (runs at 720p) and PlayStation 4 (runs at 1080p).
In an interview with IGN today, Rubin talked more about the difference.
[...]
He went on to explain that there's no agenda or definite reason for the difference. “There’s no maliciousness, there’s no specific reason why one’s 720p, one’s 1080p," he said. "That’s just the way the optimisation came out to. To keep a smooth frame rate we needed to be 720p on Xbox One. That being said, it is being upscaled to 1080p, so it is outputting 1080p on your TV, and for the most part the game does look really good. Some people actually think the textures look a little bit nicer maybe on Xbox than they do on PS4.