NCSoft isn't responsible for bad retail practices. If someone puts a City of Heroes box at Big Lots on sale for $5, then the customer returns the box saying "The game is shutdown, it can't be played at any price" and Big Lots accepts the return, if they put it back on the shelf, that's on them.
What's really happening is when games shutdown, the distributor sends a return order to retail stores: clear this title from your shelves, box them up and slap a label to ship them back to us. If they do that in the time limit, the distributor reimburses the store for every copy sent back. (Because a store has to purchase stock from a distributor to sell goods in the first place. The moment they receive the goods, the store is "in the hole" for cost until the item is sold.)
If they do not meet the deadline to return the stock to the distributor, they don't have to hold the deadline open indefinitely. If the deadline to return the goods passed, the distributor is free and clear not to reimburse anymore. The store accepts the loss permanently, and then is left with two decisions: destroy the item because it will never sell (I've done this at my past retail jobs: we got an order to destroy a dozen Windows 2000 Professional CDs and shred the license keys because the cost to ship the software back was higher than committing them to the dumpster), or slap a cheap price tag on it, put it in Clearance, and hope for the best.