HTC EVO Shift 4G

So I bought this phone for my wife the other day. I have the Samsung Epic 4G. I am used to having the program monitor where I can turn off apps that are draining the battery. Well I downloaded an app killer program for her Shift since it doesn't come with one, maybe I'm using the wrong one. It's called advanced task killer. Anyway, my issue is, after she makes a call or even when she uses an app, she goes into the task killer to kill the apps in use. Well there tend to be a lot that she hasn't even used that are running like Gmail and amazon mp3 for example. Does anyone know why these apps are running when she isn't using them and how to possibly turn them off? Thanks!