Of course a replacement is not an original. The question is, will people spend the money to buy the original.
Taffeta asked the question, why don't these diapers get such high prices as the jewellery and seaside acc.
I think most collectors don't actually buy everything they want. If an accessory is pricey or rare but possible to make a replacement of they will consider that and instead spend their $$ on items that are impossible to make.
Generally fabric acc are easier to make, it's possible to make them yourself, in your home. While with a plastic acc you would typically commission or buy from someone who specialize in it.
Well that is my theory anyway. Of course in this case it could also be the fact that a diaper isn't exactly as nice as a necklace etc.