you seem to be vastly mis-understanding what is going on.
First, nothing in Froyo disallows ATK, and it can still be used just as before. The only things it can't get rid of are the "bloatware" extra apps added which are not really running and can be ignored anyways.
Apps should close out on their own. If the app is designed to actually be able to still run while in the background though ( such as Pandora ) it should have an option to exit it in the program ( again, like Pandora where you can press Menu and choose "Quit". )
Now, WHY does froyo make it somewhat difficult to force close an app? Same reason Windows does...you shouldn't be doing it every 5 seconds! That is only a last resort if something has gone wrong. That is NOT how you just close any app.
Killing tasks is not a clean way to close an app, and it actually requires starting an app and running it in the foreground where it eats up CPU to kill the app...which the vast majority of the time the app wasn't using any of the CPU to begin with. This however is not the case with poorly coded apps or bugged apps that either get stuck awake, or are locked up. You should actually do something about these apps, rather than stuffing them under the carpet with a task killer. Remember, Task Killers don't actually stop an app from keeping your phone awake...they just stop the app for the time being. Next time you run that app, it'll try to keep your phone awake again. Fix the app, and you don't need the task killer at all.