@Mark_Spencer, Did you notice the faint right arrow at the far right of the task’s entry in the tasks list? It’s not perfect, but if a task has at least one subtask, a description, or attachment, it will appear. If it has none of those, it will not show. So it’s an imperfect indicator for you (but maybe better than nothing!) in that you can only be confident there are no subtasks if also there is no description or attachment.
Additionally, I discovered there’s a bug in Asana if you remove the last subtask it fails to clear the arrow for an otherwise-empty task. But if you add a few characters of description and remove them, it does then clear the arrow! I just reported it to Support.
Asana2Go & Trilogi Software: Asana Consulting