I just got the iPhone SDK 4 and I\'m trying to leave off developing an app I was working on before. So I implemented both
-(void)applicationDidEnterBackground:(UIApp
This is to be expected the multitasking bar "red close button" is the equivalent of force quitting an application on Mac OS X. This is the documented behavior. Apple expects normal users of iOS 4 to simply launch / use / dimiss apps they don't have to think in terms of terminating processes or anything. The system will manage that.
Just make sure to save any important data in application:willResignActive: or applicationWillEnterBackground. Because after that you might get killed when memory pressure forces the system to clean up... Snow Leopard introduced a similar behavior for apps that use the NSSupportsSuddenTermination key in their Info.plist. An app basically tells the system that it periodically saves its data bit by bit, so that when it goes in background there's nothing left to do or very little. Unlike big monolithic apps desktop apps...