[SFF]

One of the mantras of GTD is "Plan in Projects, Work in Contexts", which means that the Project view is primarily for planning, not for doing, which is why OmniFocus doesn't automatically rearrange the tasks in Project view.

When you are "doing" actions, you should be in a Context, not in a Project. Prior to the current version, Contexts in the iPhone app were automatically sorted by Due, but the recent update changed this to sort by Project, which seemed to have caused a minor uproar. As Brian said above, a future update should restore Context view to having a sort by Due option.

Also, if you have the Mac app, you can (and should) create some custom Perspectives, which allow you to have your actions grouped and sorted however you want.