I would guess that part of the problem is that relying entire on GPS would not be practical, considering the likelihood that many machines would be located with

I would guess that part of the problem is that relying entire on GPS would not be practical, considering the likelihood that many machines would be located within large warehouses or industrial buildings that block a GPS signal. The article mentions that gyros are also used, so I suspect that the company prefers to have a defensible list of purchasers, with the confidence that this would not change without their knowledge. Similar in results to a blacklist, but somewhat more reliable from the manufacturer's perspective.