It’s a monopoly/oligopoly thing. Basically, when you have only a few that handle almost all of the housing in a neighborhood, they have pricing power. They also can create the psychology in the neighborhood. You can look at comps that say $800K all you want, but if there are ten homes in the neighborhood with one or two realtors that have them all listed between $950K an $1.1M, most buyers will start to mentally equate $950K with the low end of that market.
It’s a lot like an ipod, if you want the Apple label and not a comparable machine, you’re stuck paying MSRP, which is basically Apple’s Wish Pricing which they can currently enforce.