There's also the idea that these download prices have to reflect the cost of new software rather than old, budget titles. It's setting a precident. If everything up there at launch was $20 as a budget download, people would expect that to be the price of games. Many buyers wouldn't appreciate that they are discounted old titles, and when new titles launch at $40 they'd think the price was ridiculously high as, after all, they've bought (old games) GoW and such for $20!
It is perhaps disappointing that the savings from not having a physical media aren't being passed on, but I guess there needs to be some price flexibility for stores to sell codes at competitive prices, instead of absolutely everyone buying straight from PSN.
Has anyone done a similar comparison of iTunes albums versus second hand CDs from a car boot sale at £1 each...?