From the link you've given:
Castling can only occur if there are no pieces standing between the king and the rook. Neither king nor rook may have moved from its original position. There can be no opposing piece that could possible capture the king in his original square (you cannot castle while you are in check), the square he moves through, or the square that he ends the turn (you cannot castle into check).
Looks clear enough to me. All limitations are listed, listing all non-limitations is not required.
Just thought I'd pop in to suggest a minor enhancement on the chessopedia article regarding castling: http://www.chess.com/chessopedia/view/castling
It - like many other articles on the subject found on the internet - doesn't say anything about the disposition of the rook during the procedure.
'Couple of days ago worthy opponent became quite upset midgame, when I castled queenside. Surely the rook WAS threatened on its way through the procedure, but I had no luck convincing him that it was perfectly all right for said piece to be theatened during castling.
Just a thought, but maybe you guys could excell where others have failed when it comes to ellaborating the precise rules of castling. It'd be nice to have a direct reference to this specific aspect of the rules.
Best regards, have a nice day,
vulpes