Turning on a computer, compare the probability of an issue with the ethernet cable, ie not plugged in as suggested vs a pcb trace being broken. Given that probability do you want to handle one of those gracefully and not fry the machine? Both? Neither. And that's the point of identifying the difference. A thing that is rare and if it occurs everything is b0rked anyway doesn't need to be handled.

That individual components having to be robust on some level (what level? It depends...) to failure difference of distribution via a network connection and pcb traces is probably the reason we don't usually (but we might) refer to the latter as a distributed system.