That's common practice for most credit cards in the US. Moreover, to get that grace period back you need to have paid the balance in full for two consecutive statement periods (not talking Amazon here, just other credit cards as a common policy). These policies are why B&H pays your sales tax, why department stores offer you big discounts on your purchase at the register to sign up for their credit card – they know few people have the discipline to pay off their full balance every month, and in the end they're going to make money despite the 'discounts' they offer.
Amazon Prime membership in France (Europe?) has not much to do with a credit card membership. Shipment for Prime-declared items is free, faster than for non-Prime members, and you get earlier access to "special" offers or Black Friday deals. But, unless you deliberately WANT credit, your bank account is charged in full when goods get shipped by Amazon.
Interest rates are high in the US, across the board. Good for CDs and high-yield savings accounts, not so good if you carry credit card debt or need to obtain a new mortgage or loan.
