Whoa. The Tsukinos are even richer than I thought.

[Star Ranger4]

I think the lesson to be learned here is that Usagi's mother added a little something extra into the reincarnation spell so that everyone would be well off in their new lives.

Well, yes; my take on it is is MAGIC.  Intent comes into it in my worldview; when Serenity does her thing, its part of her intent, maybe not consciously, that they wind up in a life equivalent to what they had on the moon, so there we go.