You have to understand coach is such hell now with every seat taken, more and more morbidly obese people (taking your personal space), next to no service, etc. I'm not rich but there's no way in hell I'd fly to HI (or AK for that matter) in coach. If I couldn't afford PE/F I'm not going. With boarding time you're on the a/c for nearly eight hours. Many people are more than willing to shell out a few extra thousand for a premium seat.
Normally the 789 is a good plane for upgrade odds. But I was flying PHX/DFW on New Year's day on a 789 and only cleared at boarding because of a no show.