New Naturalists hit by recession?

I happened to look at Collins' New Naturalists on sale on ebay, and it seems that they have been hit by the recession, as prices seem to be in free fall. The market for this remarkable series has seen incrdible prices paid for the rarer editions, but it has also seen many of the volumes changing hands among 'collectors' who are not actaully that interested in the contents, buit more interested in the condition of the dust-wrapper.m The advantage of this (to my mind, silly) market, is that it has enabled HarperCollins to publish many more volumes in the series than would otherwise have been possible. It is a great pity that a similar collectors' market did not develop for the World Naturalist series of Weidenfield and Nicolson. An equally important series in my vbiew, never surpassed, but alas, no longer being published.