In the case of the Warhol works, the few who own the majority are essentially in collusion to ensure that any up for auction a) are bought by one of said party, and b) bid up amongst themselves to end on a price which is comparable to the others in the past. This ensures that their previous investments retain value, because if you want *any* Warhol, you need to outbid them.
My background is in art, and with its parallels to philately--as a collectable, an 'alternative investment', and something with aesthetic appeal--I tend to use fine art as an analogy to stamps. Not to sidetrack the thread into a discussion of art-world practices, but
The Warhol market is pretty large...Picasso is recognized as the most prolific artist, but AndyPandy is 'up there' as well...with the price that single works achieve, no one person, or even cabal of collectors/dealers could control the market I'd say. And I'd say the idea of monopolizing the market would backfire, as you'd be cornering the supply of something which sells for huge sums of money. The things that people have/have tried to corner are basic or (relatively speaking) cheaper commodities--oil (Rockefeller); diamonds (DeBeers); silver (the Hunt brothers: http://stocktaleslot.blogspot.com/2006/07/1980-silver-corner.html
). I attend the sales by the big auctioneers here in HK for Chinese art & antiques, and can't imagine someone 'cornering' the market in, say, imperial ceramics. Alternative investments don't operate the way financial markets do.
Coming to stamps, well I could imagine people thinking they could speculate in some of the 'hot' items. 1970s M/S of PRC for instance. An auctioneer told me one day, when I was picking up some purchases last autumn, that things had gone way beyond the point of "do you have X or Y in your collection?" to "how many
of X and Y do you have?"
I'm reminded of an anecdote the great Herman Herst mentioned in Nassau Street. A dealer acquaintance for years was buying up all the examples he could find of a certain Ceylon stamp, citing an apparent low printing quantity for that value, so that it would be the 'key' in the set. When the dealer passed away, the family asked Herst to 'clean out' the dealer's house. In a wooden chest he said he found the dealer's horde of "his pet Ceylon stamp" and "with difficulty" shifted it to a wholesaler for a pittance.