I guess re-reading what I said its not that clear the difference..

a normal group is automatically stacked together - you need to marque it all to select - it is really one 'object'

a soft group does not have to be stacked together the objects can be anywhere, indeed the included objects can be on different layers - therefore in order to select them all you only need to select one [apart from anything else you can't select across layers in the normal way]