I think the ASDoc tool generates output for all public and protected elements in an ActionScript class.
However, I also notice some code (from AdvancedDataGrid.as) like this
/** * @private */ private var _groupedColumns:Array;
What is the reason to tag @private on a private variable?
You're right about it not being useful in the given case, but the annotation can be used to keep things out of the documentation. I see it used on a protected method in the AdvancedDataGrid.as file and I'm sure there are plenty of other examples in the Data Visualization classes where Adobe had deliberately tried to obscure the inner workings.