Here's some food for thought:
Although MS' used game policy will bring in more revenue to developers per sale of a used game, wouldn't the extra sales from people purchasing PS4 games, as opposed to XBO games, offset the loss of potential revenue that would have been gained on used game sales? In other words, if I were a developer and had to choose between PS4 and XBO, wouldn't it be more profitable for me to make PS4 games since I would get more retail sales up front on the PS4 (assuming PS4 sells better than XBO)? Revenue on the XBO might catch up over time due to consistent revenue generation from used game sales, but money now is always better than money in the future.