I don't know for sure but I'd bet that Vref prices are high becasue the
dealers who report sales tend to either report them too high or they ONLY
report the ones that sell high.

Vref and Aircraft Blue Book get their data from dealers who report sales to
them. It serves the dealers interests to keep prices high, so they serve
themselves by mis-reporting aircraft sale values in such a way as to inflate
the Blue Book and Vref prices.

Just a theory.