Sometimes it's the users and their settings. But sometimes, as I mentioned, it's the phone and/or the iOS. Nothing is done differently, either by settings, newly downloaded apps, or even open apps. But after an update, the phone starts acting differently. Sometimes for the better (ie. better battery life), sometimes for the worse (ie. worse battery life). Trust me, I've tested it. On previous phones, I did nothing with it, other than reply back to texts (didn't even launch any apps or check email) for about 3 days. And I found my battery draining much faster than before. Even after 3 restores from new (which includes downloading and reinstalling the apps I had stored, from scratch), with no resolution. The only time my issues were resolved was when Apple finally upgraded me to the iP4 (after going through 3 3GS's). It came with 4.1, and apart from the wifi issues, I didn't experience anymore issues. Hence why I'm so reluctant to upgrade to the latest iOS. I'll be holding onto 4.1 till I upgrade to the iP5.
So there is no clear cut answer or explanation to this, I've learned to accept it is what it is, when it is, for who it is. Only Apple really knows what the problem is, but they are tight lipped. Fan boys can huff and puff all they want. But the fact of the matter is, there are people who are experiencing issues and no matter what tips they follow, can't fix it. It's easy to say someone is imagining it when it's not happening to you. But I'm sure as soon as it does, they will be the first to cry foul. lol