You know people always say that M rated games can't be bundled here in the U.S., but no one ever has anything to back that up (other than the fact that everyone else always says it). There certainly isn't any law. Microsoft did bundle Halo with the Xbox . And Nintendo offered RE0 as an option for the GC.
Now of course people will point out that RE0 wasn't actually bundled with the system, but I think the point is that if there's some sort of retstriction that's so easy to get around, it's pretty useless. Because all they have to do is offer a non-threatening alternative that no one would choose anyway (a free copy of GTA or Gameday).
I really think the only thing that stops hardware makers here is that some retailers (Wal-Mart and Toys R Us come to mind, which represent 1/3 of video game sales in the US combined) don't want bundles that might turn off parents, and stocking multiple bundles is kind of a stop gap soltuion that adds more of a hassle.