I think that is due in large part to the certainty factor. Go to three dealers and their KBB numbers will all be the same.
On the other hand, it is not unusual at all to see real estate appraisals on the same property that vary by a huge amount. Just look at some of the lawsuits that have hit the press over the past few years for examples.
As far as I know, the appraisal organizations haven't touched on this issue. IMO, because the answer is expanding standards which requires:
1. A lot of work:
a. They don't want to spend the money, even if they had it, to hire the right people to write the standards
b. Such people don't really exist.
i) And if they did, they wouldn't have the conceptual framework (below) or
ii) The software toolset to get the job done
to completion.
2. A conceptual framework to complete the circle on the standards around a total objective and logical basis for a final value conclusion.
a. How do you get past estimating adjustments for features such as condition, quality, view in a totally objective manner? It's not an easy problem to solve.
So, all we have been getting and all we are getting, by and large, is a lot of the usual BS reformulated in creatively new jargon.