When you're making a new movie, the production of the master copy can cost millions of dollars. Same thing with software products, songs, and digital photos. However, making a digital copy after that is very cheap.

Therefore, it's better to say that the marginal production cost moves towards zero instead of the total production cost, which would include the master copy cost.

Well then, the price of a good is nowhere near reverting to its cost of production, which is obviously far higher than the cost of the Nth copy of that good.