The fare rules discussion is actually quite interesting. Many fare rules date back over 40 or 50 years, as you can clearly see in the UA fare rules. Many of the UA allowable connections are there because cities used to be focus cities, hubs, or it was the only way to get from point a to point b. The newer airlines (or newer routes) often have much cleaner fare rules (such as the AS fare above).

Now, it seems that these complex fare rules (like UA) primarily benefit mileage runners!! I'm surprised that they have gone away like the DC-6!!