In our case, the 'changes' would be installed on a customer's server in their office.

But you're actually totally right.

There's an interesting lawsuit (still ongoing AFAIK) involving Free, a French DSL provider. They distribute a router (those are referred to as Box in marketing terms in France) with interesting features and based on Linux. They also include many other FOSS.

It turns out they modified parts of those software (I have no idea which exactly) and are being prosecuted based on the fact that their devices, distributed to customers, include those modifications. They argue that they lend the Boxes to customers but those remain their property.

While arguing about the lawsuit with a fellow, I realized he had no idea about what the GPL actually contained.

This is an important point that I think a lot of people don't understand.

Even respected people in the technology world don't recognize that the GPL is not a use license.