[/quote]I honestly don't think Nintendo could get away with something like Xbox live without some moron deciding to file a class-action lawsuit because their little brat was allowed to have contact with some person on the other side of the planet, who may be (but probably isn't) an evil child molester.
I think you're overestimating the ease with which lawsuits like that actually get off the ground. The fact that, to date, there haven't been any even remotely successful lawsuits of this sort speaks for itself - I'm not aware of any at all, in fact.
More likely, Nintendo is worried about their image rather than potential lawsuits. Which is too bad, as I think they're hurting themselves more than they help.