If I'm not mistaken, Kancolle's money-maker is probably from marrying multiple shipwaifus (and the whole multiple construction thing?). Since you only get one free wedding ring and all.

But the point is, both games are freemium-friendly and are successful because of it, just that they go about it in different ways.

Almost all games are pay-to-waifu though. Just Kancolle is more of a pay-to-multiple-waifu.