Moore's law again?
I guess it's due to the fact that the mighty chip companies are now concentrating on producing DDR2 chips, leaving us DDR users bobbing about making use of obsolete memory. The economies of scale are - understandably, I guess, being found with the memory which is in most demand by the Dells of this world. They probably are still producing DDR stuff, but, being old hat, aren't trying too hard to reduce the cost: the volume's not there any longer.
Make sense?