It's different with something that is written about decades in the future (at least at the time it was written). It's just when you're talking about things that are in the near future, like the Voyager probes, I thought they'd want to try to make it a bit more realistic.
Again: Nobody in 1978-9 would've found it remotely unrealistic that there could be more
Voyager probes. If anything, they would've probably thought the opposite. There were over ten
Mariner probes and
Pioneer probes, and a whole bunch of Russian
Luna and
Venera probes. So the idea of a probe series stopping at a measly two would've seemed ridiculous at the time, in defiance of all precedent. They'd lived through two decades of a relentless, active space race, and had no idea that the brakes were about to be put on by budget cuts. So they would've assumed that space exploration would continue at the same rate as before. They would've had no reason to think otherwise, because they didn't have your after-the-fact knowledge of what actually happened. It's always a mistake to assume that the way you see things is the same way people in the past saw them.
But in all seriousness, I just feel if you are depicting something in the very near future, I'd think you'd want to try to be a bit more factual. That's the difference to me.
But why? Stories in the present aren't required to be "factual." They make up imaginary people, imaginary cities, imaginary countries and political leaders, and imaginary world events and crises and disasters all the time. There's good reason to
avoid telling stories about real things, because doing so runs the risk of legal entanglements as well as conflicts with reality. You
want to keep your distance from real things so that you have the freedom to tell your story. Heck,
The West Wing not only had a fictional US president dealing with crises in fictional foreign countries, it even displaced the election cycle by two years.
And stories set in the past aren't required to be factual either. They tend to be built around real historical events, but populate them with imaginary characters and reinterpret the facts and chronology of events to suit the needs of their stories. Even movies about well-known historical events, like the Gunfight at the O.K. Corral or the Untouchables' battle with Al Capone, are usually based more on the myths that have grown up around them than on the strict historical facts.
After all, fiction is not
trying to be real. Realism is not the same thing as reality. It's all pretend, and that's all it's meant to be. If you tell your pretend story in a way that gives it a realistic flavor, fine, but it's not trying to convince anyone it's
actually true, because that would be fraud, not fiction. If you use elements of reality in your story, that's not an end in itself; it's just a means to the end of telling the story you want to tell.
Now we in the US are in a situation where China and Russia may overtake us in space and now we have to play catch up. It was a bit short sighted of the politicians to sort of give up on space exploration if they want to think in those terms. It's sort of embarrassing I think that we have to hitch a ride with the Russians to even get to space now.
Nationalism is a ludicrous and petty mentality in the context of humanity's expansion into space. It doesn't matter
who gets us there as long as we get there. If we can establish permanent human habitation in space, then we preserve our species's survival for potentially millions of years to come regardless of what disasters may befall the Earth. Our descendants won't remember or care which national flag was painted on the ships that did it, because nations are ephemeral constructs on the grand scale of time. All that matters is that
somebody gets us out there for keeps.
And of course it probably won't be national governments alone that get us out there -- it'll be a partnership between government and private industry. History shows that the settlement and development of a frontier never really takes off until that kind of partnership emerges, with the latter taking the lead in developing the profit potential of the frontier, bearing the risk that a government alone isn't willing to take. We saw this with the fur trade in North America, the East India Companies in Asia, and elsewhere. We can now see the beginnings of the new space race, the
real one, driven by private businesses pursuing profit opportunities like asteroid mining and space tourism. Once space becomes profitable, that's when colonization will really take off.