It usually happens to people after they have done something specific like an upgrade or, like you, added an account. When you first add an account it will use a lot of power the first day just synchronizing with the Exchange server, but that should be a one-time event and, unless you have a huge inbox or you are syncing multiple folders, should resolve after an hour or two. But it is logical to think "I did X and the result was Y". It's only when you compare notes with hundreds of other users that a pattern emerges. In spite of the large number of reports, the problem is rare considering there are over 100 million iDevices. It's usually people who are power users who experience it, however.
I'm speculating now, but I think it is caused by doing something that interrupts an Exchange update before it completes. When the device resumes from the interruption there was traffic queued on the connection, but the mail app doesn't know about that and opens a new connection. Meanwhile the lower level protocol is still trying to complete the exchange on the now dead connection while the mail app is using the new one. Clearly installing an update could coincidentally interrupt communications. So could a sudden signal loss, or switching from cellular data to WiFi, or rebooting the phone (which Apple says not to do without turning it off first). Just turning the phone off should not, because a power off condition notifies all of the active apps that a shutdown is about to occur and gives them time to "clean up." That's why the circle spins for several seconds after you "Slide to power off".
The same process can result from any app that uses data in background, but those are harder to fix, especially if it is the built in apps like Game Center, Ping, App Store, iTunes Store, etc.
As to whether it's something that Apple could fix, I don't know. In theory it could close all connections periodically, but there is then the risk of losing data. I do know that other smartphones have similar problems, (check the Android or WinMob forums) so it certainly isn't an easy thing to fix.
