By your reconing, these are all railroads because they have some set of consequences for failure to act. By your definition, life is a railroad.
I've noticed that there are many straw man arguments here.
I have said repeatedly that event based games put pressure on players, and IMO a railroad is when this pressure is intolerable. A racetrack or highway is not a railroad, but it sure is more of a railroad than a parking lot is. Some players want to go off road, but they either aren't given the right vehicles or the terrain is presented as unpassable, or just less pleasant than their expectations of a good time.
All fine and good. You know who else has self-motivation? Every single NPC, including the villians.
This is where the setting makes a big difference. If the world provides more motivation for villains to act then their choices will overshadow those of the PCs. In darker times it's the heroes who want change, not villains. At least, it's not very difficult to create a realistic setting that offers this.
That's still GM fiat. Changes in 'normal' RPGs only happen because the GM causes them. That may be triggered and determined by player action, but only the GM makes changes. The question you haven't answered is why only the players get to determine this. Why is the GM in your view nothing more then a computer cranking out quests like so much CRPG?
Well first of all, the GM has to setup the status quo in the first place.
It's funny that you say the GM is a robot. If anything, I think the DM has to be MORE creative in this case. If the villains and events are happening independent of the PCs actions, then anyone can develop this for the DM. He can just pick up a module, or adventure path, or railroad, or whatever and crank out the world as given.
A sandbox GM has to be more reactive. Instead of plotting doom to the setting, he gets to make changes to the status quo in a positive way as the PCs improve the world. I think this actually fosters a more cooperative relationship between players and DMs and inspires fewer meta game attitudes, munchkinism and 'us vs them' attitudes.
Speaking of munchkinism, this style of play also makes it easier for PCs to choose their own challenges. It's just a matter of understanding the world around them and avoiding areas that are seen as too difficult. This lets the PCs make whatever type of character they want, even if it's not completely optimal. The DM is not the player's adversary and is not plotting their doom. Instead, the players are the ones risking their characters for the betterment of the game world.
There's that false dicotomy again. Who said coast? The players have to engage in the plot, follow hooks and leads, address the conflicts, and overcome their challenges.
Like I said, there can be a lot to do on a train. But you're not the one who is really driving it. The DM is moving the world without you while you coast along.
That's why a status quo world is boring. The players choices don't matter because nothing happens when they aren't around.
First of all, you can have excitement within a world even if it's static. Second, player choices matter even more BECAUSE nothing happens when they make no choices.