What's the commonality between all the places you listed?
They're all modern day places that are big enough that I recognized the names. It's not like Sharon Springs, N.Y. (for example) is on that list (and while Sharon Springs has a small town feel to me, it's population is MUCH larger than 70, and certainly not everyone knows each other). Crime in small towns is much less common than in a big city, in large part because of the close knit community such places naturally encourage. That applies far more in a medieval-esque setting, since in such a world you can't just hop into your car and head to the big city for a few hours. You're isolated, and highly dependent on your neighbors for survival.
Killing for the money and remaining in town is a bad idea because if you've killed someone then you've weakened the town's ability to survive as a whole (and you are part of that whole). You can't even spend the money to improve your lot significantly, since word gets around in a small town and therefore if you spend it everyone will know what you did.
Killing for the money and leaving is a bad idea because then everyone will know what you did. Assuming there is any kind of system of justice, once word gets out you're likely to be in real trouble. You could maybe hide out in the woods, but you can't spend the money there and your life is going to be significantly worse than if you'd never stolen the money in the first place.
It could occur as a crime of passion, but that's going to be rare. People who are willing to kill a friend or family member over something like $10,000 are the exception rather than the rule. Based on my personal experiences, that's likely doubly so for small town folks, because from what I've seen they care about how they are regarded by their community. While crimes of passion aren't rational, they are heavily driven by our passions. You might be angry at the elder for not giving you more of the money, but those emotions are likely to be tempered by fear of the community's reaction if you were to step over the line. You're not being tempered by your rational mind, but rather by your passions themselves.
That's my take on it anyway.
As someone who lived in small towns for about half my life this is very true.
Everyone knows everyone. Even the kooky old guy who lives in the little cabin 20 miles from town up the mountain. And we don't just "know" them in the casual sense of we're familiar with their face or their truck. We
know them. We know where they live, we know who their mother, father and grandfather is, and in a very real sense, in
very small towns most of the town is usually related to each other. New blood is rare. Small towns often have 2 or 3 "major" families that make up the bulk of the town, who are usually related. There's a couple of smaller families who make up the rest. So it's not even that you would be theoretically stealing from a guy who knows your face, you're stealing from someone who is possibly your aunt or uncle.
On top of that, it's not just that was know who you're related to, we know where you work. We know your extended family lives in OtherTown down the river. We know a lot about pretty much any given member of society because we all work together, eat together, sleep together (both Biblically and metaphorically) and attend the same house of worship together.
People who live-in-town certainly DO commit crimes against each other, but usually as a result of drunken idiocy, youthful arrogance or long-time grudges. These are not master criminals with well-thought-out plots of how to steal the money and run off to CityVille and make a new life for themselves. In all of those cases, everyone knows exactly who is responsible. There's no "whodunnit" element. And to be honest, most of the "crimes" in small towns are social ones, not to put too fine a point on it, but I'm talking about sex. Married person gets drunk and sleeps around. Young punk things they know better and knocks up the Pastor's daughter. Larry hates Moe so he sleeps with Moe's best friend Curly.
In fact, a small town (even IRL) could probably tell you about the last time someone actually got killed in their town. Small towns don't have much (or get much) in the way of news, but oh boy do they have gossip!