Don't know if it's been mentioned yet, but I realized why Sony's still charging full price for digital copies of the retail games that have dropped to $20 (eg Wipeout)
It's because it's a clearance sale, they're trying to get rid of stock, and if people buy the digital copy, all those retails boxes will just sit on the shelf. I would hope that by the time Christmas has come and gone, the digital versions' prices will drop.
Sony probably figured this out as a new problem with digital sales. Sure, they are saving money a little bit on digital sales, but if those retail boxes just sit there, or get returned, it'll probably balance back out and they'll lose money cause the cost of production didn't actually go down.