Alternatively, Ghost Ship could have said "Each other player puts cards from his hand on top of his deck until he has 3 or fewer cards in his hand."
This is what I meant. Why didn't it use this wording, which is more concise and consistent with other cards like Militia?
Ah ok. Well "or fewer" would probably lead to some rules questions I think.... for one, a new player would be confused as to why it's there, since it makes them think that maybe Ghost Ship could cause them to go below 3 cards.
Also, depending on exactly how you read the rules, it isn't completely clear that "or fewer" would solve the problem... if you read the instructions in order, then you would put 1 card back, then check to see if you meet the "3 or fewer" requirement... meaning that if you started with 3 cards, you might think you have to put 1 back still. Although to be fair, Library and the others have this same thing.
I dunno, it's inconsistant, but I think Ghost Ship wording is clearer.