The Oxford Style Guide uses the serial comma convention, while the Chicago Manual of Style, the AP Stylebook and The UPI Stylebook do not. However, in those that do not, there is a specific exception to clarify ambiguities.
This is entirely clear, which is no doubt what ought to have been written:
The canning, processing, preserving, freezing, drying, marketing, storing, packing for shipment, or distribution of:
This is also entirely clear:
The canning, processing, preserving, freezing, drying, marketing, storing, packing or distribution of:
But it has a slightly different meaning, if there exists the activity of packing for reasons other than shipment.
Of course, with the comma missing from the original language, one can argue that "packing for shipment or distribution" is an activity that doesn't include the actual distribution, which no doubt is the basis for the case. However, I think in the end the meaning that is clear when the comma is included will prevail. "Packing for shipment or distribution" suggests that there are two separate packing activities, one for shipment and one for distribution. It seems most unlikely to me that the plaintiffs will be able to prove that these two activities both exist separately in their business, so that meaning wouldn't have any reference in fact. Therefore the meaning that would be clear if the comma were included will probably be found to be the correct one.
If I ever find myself drafting legislation, I shall keep the Oxford comma scrupulously after seeing this.
An unforeseen consequence of the information revolution has been the exponential propagation of human error.