I think there's more to it than that see my experience below:
I've spent a lot of time on this, so will try and summarise.
I have an old (3yr-ish) iphone 4. Although the battery was well used, prior to the 6.1.2 update it would last from 7am to midnight with no problem. Usage was calls, text, hotmail and Words with Friends, not much else.
Immediately after the 6.1.2 update , the battery started to drain very quickly, it would last maybe 4-6 hours. Nothing else had been changed on the phone.
I followed all advice I could find on the net, and ended up restoring as a new device, installed no Apps and didn't configure hotmail. Still had the same problem, although it might last an hour longer..
Waited a few weeks and installed 6.1.3. Same problem.
Spent two days on the phone with a very helpful lady from Apple California to try and resolve.
Basically, I reinstalled the phone as a new device and monitored.
Couldn't improve the situation.
Went to apple store. They checked it out and said something strange was happenin, with the battery readings on their diagnosis software, some sort of mismatch that might be resolved with a firmware upgrade. ( sorry, I can't remember exactly what it was!). Firmware upgraded, same problem.
Advised to get a new battery.
New battery installed and things have improved, my battery now lasts from 7am till about 7pm. I have no apps installed and only have light call, text and hotmail usage.
I am using it less than before the update, I have a new battery and still have less battery life.
I have another friend who has experienced battery drain and a couple who haven't (iphone 4 and 4Ss)
My conclusion is this:
My original battery was not as good as it used to be.
A new battery is much better.
IOS update 6.1.x is probably much more battery Hungry than previous versions.
It appears to absolutely hammer a specific group of iphone models but not others, maybe a certain batch/chipset/firmware version or mix of the three.
If this doesn't affect you it doesn't mean there isn't a real problem, it is very frustrating and disappointing.
I guess at some point apple will sort it out, when they do, I might buy an iphone 5, otherwise, I feel like I'm being pressured into it!!! :)
Good luck