Big difference between typical business and this issue is Sony trying to retroactively charge people top up money on things they already bought at a deal price where they are trying to get gamers to pay top up fees.
If Sony (or any company) wants to charge people the difference in fees between product x and product y, go ahead if that person is buying it right there for the first time. But when people have already bought some product at a sale price, that should have nothing to do with Sony trying to get their hands on gamers saved buying it on sale months ago.
If you have a game to trade in to Gamestop, they'll off you $30 if it works and comes with a case. It makes no difference if you bought the disc at regular price, on deal, or got it for free from your brother. The deal is $30 trade in value. Not $30 plus "lets factor in what price you paid for it so we chip down the trade in if we find out you got it for cheap"