Trust me, if the used game stuff on the XB produces for publishers they will force it on sony as well. The only thing that will stop them is being sued. And good luck suing Sony. By joining their network you give up the right to sue and have to go through an arbitrator of their choice.
Similarly, if the used game thing fails for the XB, it'll be abandoned by publishers as well. I believe the design is that used games are legit, unless the publisher's decides to disallow it. If that happens, they can regulate the resale or ban it outright. At this point it's a threat but not a promise. However, it will get used by someone. Interesting to see how it'll work out.