[Tim Wood]

In Planning mode, when sorting by due date, OmniFocus sorts the projects by the minimum due date of the incomplete actions in each project. So, as you say, if you have added an action in project A that is due before the entirety of project B, then project A will sort first.

Start & due dates on groups (projects and action groups) provide something like a default start/due date for the actions contained therein -- if you set a due date for a project, all the actions therein are assumed to be due by that date, though some may be due earlier if you set explicit dates on them (later due dates will be clamped to the minimum of the due dates of the containers).

So, given this approach, there is nothing particularly special or more important about a due date on a project vs. one on an action. We still do have some UI ideas to make this more clear and friendly, but they are a little too wild to make it in to 1.0 -- maybe 1.1 or possibly not until 2.x.

In the case you mention, the project is currently more important to you, but there is nothing to say that the action might not be more important in another scenario -- OmniFocus can't make this decision for you. That said, there might be call for some sort of preference to add this behavior to OmniFocus if that's the way you tend to work. I do worry that someone might miss a due date if we take a different approach. OmniFocus is trying to be very conservative and trustworthy here, by ensuring that the project with the overall earliest due action is listed first.