I gotta disagree here a bit. I've downloaded apps in the past that would persistently do things in the background (like try to connect to the Internet) and I did not have an option in the app to stop it. This is the result of bad coding, not the Android system itself. Even this doc agrees that a task killer could be useful if you use an app that was poorly coded:
"That said, not all apps are created equal. Many of you have used task killers in the past and actually found that after freeing up memory, your phone works a bit better. It's more likely that this is because you've killed a bad app—one that was poorly coded, and (for example) keeps trying to connect to the internet even when it shouldn't. Any performance increase you experience is more likely because you killed the right app, not because you freed up loads of memory (or, in many cases, it's just placebo). Instead of killing all those apps, find out which ones are actually causing the problems. If you really know what you're doing, you may benefit from using a task killer to stop the one or two inefficient-but-loved apps on your phone."
I have ATK and I have it tuned to kill some apps that I like, but will drain my battery without an option to stop. I think you are being a bit misleading to say that task killers in every instance are worthless.
b