Personally I believe it's to improve the quality of the artifact. We all know of the Call of Duty: Modern Warfare 2: Prestige Edition with the Night Vision Goggles. Well imagine if they only made 20 copies and they were all a gift/prize for playing well in the beta etc.. Since only 20 copies are being made the NVG's could be higher quality and everything else could have a more unique feel. I believe this is what they are doing here, as this Phurba Dagger in this package could be made of wood, stone anything as when you limit the number being made the quality and amount spent on each can rise. This is mainly because the fans don't have to spend the $200+ it may have cost to make it, Mass produce these things and the Dagger could be made of a cheap laser carved plastic because they are making 400,000 of them instead.