It is apples to apples.
Benchmarks for the exact same items being resold through the exact same auction house. Time doesn't stand still, neither does the economy, so what you seem to be suggesting is that apples to apples comparisons are never possible. I would disagree.
As far as the economy goes, it is my personal opinion that there is in some ways a market "bubble" in the original prop and costume market, just as there was in the housing market (to take your example).
This is a market where it only takes two buyers on the same items to drive up prices beyond what anyone else believes is reasonable.
To further complicate things, given the Profiles in History terms published in their catalogs, we, as spectators, can't really know who bid on what anyway; or at least it isn't completely clear to me, given the following published policy...
Below is an excerpt from the Conditions of Sale from the auction catalog for The Dreier Collection:
5. Reserves. Lots may be subject to a reserve which is the
confidential minimum price below which the lot will not be sold. Although the
auctioneer may open the bidding on any lot below the reserve by placing
a bid on behalf of the seller, Profiles reserves the right to protect the reserve
by bidding through the auctioneer and continuing to bid on behalf of
the seller up to the reserve amount either through consecutive bids or by
placing bids in response to other bidders. Consignors may not bid on their
own lots or property. If the consignor is indebted to or has a monetary
guarantee from Profiles in certain circumstances, Profiles may have an
interest in an offered lot and the proceeds therefrom apart from Profiles’
commissions, and Profiles may bid thereon to protect such interest. In such
instance, Profiles is entitled to its standard commission rate when a lot is
“bought-in” to protect its interest.
Is there any distinction in the auction results published by Profiles in History with regards to those items that were bid on, but did not sell (i.e. meet the confidential reserve)?
Do "bought-in" items show up in results as "sold" items?
If so, wouldn't that portray a false image of market values, if people recognize something selling at a specific amount, when it may have actually gone unsold, as the confidential reserve was not met?
Obviously, information is power, and the auction house is in complete control of the key information regarding their sales, and it is to their commercial advantage to share only that information which presents them and their sales in the most positive light.
As a third party observer, given the above and all of the unknowns and ambiguity, I really never quite know what to make of these auctions, as the facts are limited in scope and details.
Jason