This is in reference to the table stored in the WireSizes.xml file, which is based on the NEC table referenced... but can certainly be modified if necessary to be non-NEC based.
The way I read this is that there are two options for sizing the Neutral... 1) The neutral will be the same size as the Hot conductor, regardless if there is any current in the neutral, or 2) The neutral will be sized based on the current in the neutral (using the WireSizes.xml file for the table lookup).
I spot checked the referenced table in my 2005 and 1996 NEC and didn't see any differences.... the user could modify the WireSizes.xml file, if necessary, to provide adjusted values to the table.
I haven't tried sizing wires to compare the two methods yet... if I find anything contrary to my expectations, I'll post a follow up message.
Martin Schmid, P.E.
Martin Schmid, P.E. Product Manager - Revit MEP Architecture, Engineering, and Construction Autodesk, Inc.