Have you guys actually been using the phone for the whole time.
I was finding that my 4S was always reporting usage was half of standby even if I hadn't touched my phone.
Ive now had it replaced and can get 2Days 15Hours standby with 4Hours of usage.
I can also get my phone to behave the same way as my old 4S.
I recreated this behaviour by opening a picture in Facebook.
I am going to try opening other Apps to see what other ones start to replicate the behaviour.
People having issues should try rebooting there phone and re-introducing the use of apps one at a time to see if they can replicate the issue.