I think it is also a "product cycle" that we see with big sellers. There seemed to be some slightly shady business with this one however. The 540ES was occasionally on sale direct from Sony at a very low price and people were trying a short while back to flip them for a profit. Not sure what this might have to do with your question.
What's with all the Sony 5400ES units for sale?
I figured this unit was one hot item, if you read reviews and owner comments. So why do we see so many used players for sale? I've read that the break-in time is quite long, and maybe the satisfaction quotient makes folks give up on it too early? Or maybe this player isn't really the cat's meow we all hear about. Any thoughts?