it would be nice if they did that automatically! i'm guessing they don't because you don't have to necessarily use tasks on projects they didn't bother? but we've had to script it in the past when we wanted that behavior - not sure if it would be available for workflows. maybe if your users use 'time tracking' instead of weekly timesheets you could do a WF? but not if they use weekly timesheets, as those "sublist" list of time entry aren't available for WFs.