Actually, nobody even went as far as saying "latinum can't be replicated".
For all we know, it can, just like hundred-dollar bills can be printed.
Latinum is not a currency, it's a rare material, like diamonds. That's why it's important that it cannot be replicated in a proper fashion, because otherwise the entire Ferengi financial system would fall apart. There might be artificially created industrial latinum, like artificial diamonds, but just like those, it's useless on the market.