Automatically Adjust Parent Tasks Based on Subtasks

It would be great if Parent tasks worked better to summarize subtasks:

When subtasks are all completed, the parent task should automatically be completed

If all subtasks aren't completed, then you can't complete the parent

When subtasks dates are changed, the parent task should also adjust

etc...

I personally can't see why the current behavior is usefull to anyone, but in the even that it is, just give us a setting somewhere "Link Subtasks to Parent Tasks" that adjust the old behavior to the new