similar items happen in the NY area. JFK, LGA, and EWR are within spitting distance (I can spit pretty far), but the fares can be different by hundreds of dollars. I think this is becasue loads are generally per flight and it would get very complicated if they had to look at neighboring flights or airports and adjust fares. One flight change could result in hours of work for recoding all the neighboring flights.

At SNA, there have been two scheduled US Air flights leaving within minutes of each other to PHX with price differences. usually <$25, but still interesting to see.