I think you're confusing that with Android. In Android, the background programs remain running, sucking up battery. This is traditional free-for-all multitasking. Every program that wants a slice of CPU gets it.
In iOS since version 4, background programs are suspended by default, don't take one cycle of CPU time. There are limited exceptions: audio programs can play audio, VOIP can process calls, and an app will be allowed to complete certain things it started (such as a file download). There are a couple others, but you get the idea.
So if you're running Skype and audio in the background while playing a game, yes, your system may be taxed and the battery will drain more quickly. But if you have IMDB, Safari, Chess, etc., in the background, they're not draining your battery because they're suspended.
Beg to differ, I never have had an Android, only iPhones. If I don’t go in and shut those programs down as described the battery runs down fast. Otherwise it lasts a very long time. I didn’t have to go in and shut programs off in my iPhone 3G and the battery latest all day, no problem. Only my new iPhone 4S has given me battery life problems.