See that's where you aren't 100% right. Sony, as a publishers not force any restrictions. They does not mean Sony, the hardware maker, will not have a system for DRM on the PS4.
Let's look at what we do know. Sony has said the PS4 will not be always online and will not have an online DRM and games from Sony will not force any restrictions. So end of story, no DRM, we get used games and all is right with the world. Well as Lee Corso would say, not so fast my friend!
As we learned about early this year, Sony United States Patent Application US20130007892, Sony's technology would check a game disc's RFID tag, which is capable of remembering if that game had been linked to a different machine or account. This check is performed offline and before the game is played. So once a game is placed in a PS4, it is locked to that system and cannot be used in a different PS4.
Yes, Microsoft and Xbox One is taking a lot of heat for its online DRM. Microsoft may have done this as a cash grab but it does seem like, more and more, this DRM push is coming from the publishers and not Microsoft. Again, I'd wait for all the info to come. It may not be Microsoft or Sony forcing this.....