The default value refers to what the field will default to when a new step of that action type is displayed in the GUI (and stored in the .bld file if the default is used).
http://www.kinook.com/VisBuildPro/Ma...propguitab.htm
For radio and combo property types, a value of 0 (the first item in the list/radio) is not stored in the .bld file and it will default to 0 when retrieved.