It feels to me like your initial intuition was right - they are being jerks/babies and they aren't respecting the decisions their past selves have made.

I went through a phase of tongue-in-cheek "quantum planning", wherin I would give my friends a percentage on any plan I was invited to. So if I was asked to dinner I might just say "60%". Needless to say this didn't go down very well with people.

There is a value to your word, and yes, it is more prevalent in closer-knit communities than in bigger cities, but I think that's because the cost of ditching a "friend" in a big city is much lower - after all there a plenty more potential friends to be had. But in my opinion someone who habitually breaks plans is giving a clear indication that they don't value their word and don't value the person they break plans with.