Unfortunately, that is all true, due to the embargo / OFAC / "el bloqueo". US-issued credit cards are not accepted anywhere in Cuba for any reason; one can not earn (or spend) points or miles in US-based schemes (or if your account uses a US residential address) for any travel in, to or from Cuba.

With currency-related issues, as the US Dollar is not accepted and there is a significant surcharge for exchanging US Dollars to CUCs, it's a very good idea to take Euros for your cash expenses (in my experience) - and I have heard Canadian Dollars are nearly as acceptable.