Well I just read the 'details' (when in AutoKiller hit the menu key, click settings, and at the top you will see 'Home page'... click it and at the end of the very first paragraph you will see 'details', 'process manager' and 'FAQ') article twice, and while I understand it in my own head, I don't exactly know how to explain it on here to where I could help you understand it at all I don't think. I recommend reading it yourself (it is quite lengthy, but very informative) as it really does a good job at explaining how the whole process works.
And one thing expecially that I got out of it, in there he explains the way Android differs from Windows and even Apple... Android systems are built to keep apps running in the background, like that's their whole philosophy. They do this to keep things open so that if and when you go back to that app, BAM it's right there. So the whole Android process is run by a manager that finds value's for the apps importance, and when you start running low on memory, it will kill off the apps that are least important to you.
After reading that, I really understand just how anti-Android ATK's really are, and why Google disabled them in 2.2. Apps are supposed to be running in Android, if you kill them off then you might as well be using a Window's mobile device. Read that article, it's really informative.