Royal
Connoisseur of Exotic Pictures
Yeah except being unrated or even nc-17 is a defacto ban. Fuck the MPAA and fuck everyone who keeps the rating system in place.
That has more to do with the consolidation of the theater industry into a handful of mega chains that have to be placated than anything else. And those chains wanting a standard system for audiences to be able to use as a guide. There's enough of a demand out there from that audience that another rating system would just replace the MPAA's if it were to ever go away (and in fact others do, they just tend to be more narrowly focused in their standards).
Besides, with the critical success of Saving Private Ryan with it's R rating do you really think Christopher Nolan felt the need to avoid going past a PG-13 or was pressured not to by the studio? The dude is a god in halls of Warner Brothers.