Technically you are both right and wrong. 720 was the original beginning to HD, but that's no longer the case, 1080 is now the lowest resolution to meet the "true HD" specifications. 720 is sort of like the "standard" definition of HD. and no, I was in no way thinking of 480, I come from a film and production background and could in absolutely no way confuse the two lol but it's the same with 720 to 1080, I can in no way confuse the two. And there's a reason why you're not seeing much difference between Ghosts on the 360 and the One... because it's still upscaled since the One is not native 1080.. lmao
There's a dramatic difference in clarity if you compare the 360 or PS3 version to the PS4 (I'm not talking shadows, I'm talking crispness and color clarity) because the PS4 version's native resolution is 1080 and has to be downscaled for TV's not 1080 native.