The Jbpm process can handle the manage the persistent state changes. Normally with a process your indvidual tasks would be a bit larger, but there is really no reason that you couldn't simply show your tasks as links which signal the process. Look at the task list components for how to show the tasks and create proper links. You can start/end tasks with annotations or in pages.xml.
It's really a very straightforward and simple use of jbpm. I don't see anything too complicated there.
My understanding is different.
For instance once the author of a document completed with draft it might ask somebody to review the document. And the process of reviewing would be a normal business process. As the result of reviewing the document could be promoted to the next state. But, when it is being promoted the action assigned to the transition could perform whatever we want, for instance inform the people interested in the traking the document about the the fact that the document has been promoted. That's why I believe jBPM suites.
Lifecyle is similar to state-diagram or timeline (It's matter of taste). I'd prefer not to see tasks in the Lifecycle graph.
And what is important user can be happy looking at the picture. Tasks make the picture overcomplicated.
Yes, jbpm fits it. Several of the example apps use Seam's jbpm integration to do very similar tasks. It works quite well. I think you'd want to do something similar to the DVDStore, except you want the UI to be more elegant than the very generic view there.