Both are for people unable to resist fluffy cute goodness of nappies...
The Wagon is for people trying to stop themselves buying new nappies because they can't afford any at the moment, have enough really, partners are beginning to wonder who their wife/etc loves more the nappies or them, they have no more space etc
The train is for those who have/want no such constraints, the nappy train stops at many wonderful sites/sights along the way
Hope that helps confuse you less!!