It is very bizarre that Viz Media will publish quite violent manga (heck, even the Bleach manga has a fair bit of blood and limb-removing action) yet they obviously won't publish something due to sexiness. I could kind of understand them possibly wanting to avoid publishing To Love Ru Darkness, but I'm fairly sure they could get away with publishing To Love Ru under their "Shonen Jump Advanced" tag, possibly with an "Explicit Content" note on it.
Thanks for the tip about it being published in Spain and France though. I'll probably order the French volumes then - will probably be cheaper than getting the Japanese volumes and I can buy Darkness without fear of customs xD.
And I'm so glad I ordered the American Shana II release now. I think black amaray cases look absolutely horrible.