Many manufacturers serialize the barrel and the receiver and while it might some applicability to parts logistics, it is primarily about universal law compliance. Glock, HK, any manufacturer with a large international market will, as much as possible, legally universalize any gun they make.
In America, obviously, the receiver is the "firearm", but in South Africa and many other countries, the barrel is the legal firearm and hence needs serializing. Benellis are serialized in several places so that all guns are universally compliant with regard to the actual serialized "firearm." This way any gun can go anywhere and have the correct part properly serialized pursuant to that country's law.