You must work at Lion Head Studios or something. The budget has a lot to do with it, sure it might take a developer there a day to make the weapon, but that's a whole day of work they would have to pay the guy.
Lion head would be making money from setting up special deals with game companies like EB and Gamestop and what not to add these special weapons into the game. Now would it be fair for someone to just go and trade a special edition weapon to someone who didn't pay the full price to get the special edition of Fable. 50 weapons is what they said they had to make, if you didn't read the quote in the first post, and 50 weapons is what they made. The bonus weapons would be whatever didn't make it into that list and bundled with the special editions. Not being able to trade these weapons is not a big deal at all. Just move on and go find the other weapons that are actually in the game.