AFAIK all airlines will let you standby for the next flight if you miss your flight and show up at the airport within a reasonable time afterward. So if you want to play the "buy cheap, fly expensive" game, book the flight before rather than the flight after.
US-based airlines offer this. Many others around the world do not. And with some in the US it depends on calling in before the original flight leaves.
jetBlue's "immediate previous flight" rule for free standby is an interesting one because it includes connections - routings that might not actually be any more convenient - rather than looking only at the same routing. I actually think that they are unique in this approach, though some other carriers do not allow change of routing for standby, so the rules really do vary based on carrier.
As for the "plane goes out with empty seats and someone will never fly the carrier again" theory, if something like this is enough to put them off of jetBlue I'd hate to see what happens if there was actually something bad happening.