The primary objective of the dropdowndatawindow edit style is to link the column from the main datawindow to the primary key column of the dddw (Data Column) in order to easily obtain the value of one of the other columns of the dddw (Display Column) which would normally be the description of the record from the lookup table. The dddw edit style automatically fetches this value for you and places it in to main datawindow buffer.
If the case is where you have additional columns in the dddw that you want to access then Lar's method is the correct one, although to achieve the same objective I prefer not to define additional columns in the dddw but to instantiate a separate datastore which I'll use to fetch the complete record of the lookup table and grab the information from there.