Given that I've personally bought Cuban cigars with my Amex card last Christmas as gifts, I'm pretty sure your assertion is false.
It's more likely the case that an American credit card holder cannot buy them, even when he is in Germany, because he's subject to American laws, as I would be if I took a box into the US and started selling them.
It's more likely the case that an American credit card holder cannot buy them, even when he is in Germany, because he's subject to American laws, as I would be if I took a box into the US and started selling them.