Shonen Jump magazine is rated all ages in japan because it teaches kids-teen about friendship. While in other states its rated 13+. I mean is it so bad for childeren under 13 to read it. My little bro is 7 and he likes shonen jump. Give other kids the chance to read it. Im glad i was born in japan though
I think you're missing something here - we don't have ratings for publications in America. There are laws against indecent public display, which prohibits a vendor (or anyone, really) from selling something like Playboy to people under 18, but it's not like the game, music, or film industry, which are mandated to have ratings. Viz (which publishes Shonen Jump), simply rates their comics out of common decency to parents and lazy sales people who cannot for whatever reason make judgement calls on their own.
So, now that you know that such ratings don't exist in either America or Japan (so you're wrong about it being rated 'all ages' in Japan), you can go to Viz's website which explains why each thing is rated what it is:
http://www.viz.com/ratings/
Cigarettes and alcohol are instant 'Teen' ratings, so for all you care, it's the fact that Sanji smokes in One Piece that gets Shonen Jump a teen rating.