I haven't been around as long as other people, but I've never seen error fares on anything but the legacy carriers. I've seen them on all the legacies as well as large international airlines, but never on Alaska, Southwest, or jetBlue. I believe there could be a couple reasons for this.

1. Their routes aren't as large and complex. With hundreds of thousands of different route combinations, alliances, currencies, etc. there's more likely to be a error somewhere.
2. Error fares do occur but are quickly corrected or never last long enough to make it to the blogosphere.

The closest thing to an AS error fare was the Iceland currency conversion which allowed you to buy miles for cheap on their partner Icelandair and then redeem for flights on AS. Its been a while, but if I remember correctly you could buy enough miles to fly first class to Hawaii for a couple-hundred bucks. With the way the USD is going right now I'm somewhat hoping we'll have another opportunity like that soon.