These are big, popular games. When asked about the decision, the company told VideoGamer: "One of the many benefits of Amazon Prime is access to exclusive selection on a number of great products. Customers who are not Prime members can sign-up for a 30-day free trial of Amazon Prime, or they can purchase those items from a Marketplace seller." Amazon has taken a similar approach with other forms of media -- in the UK, for instance, you need a Prime subscription to buy Spectre on DVD.

Amazon has used games to drive Prime sign-ups before. In the US, you can get up to 20 percent discounts on pre-orders and newly released games if you have an active subscription. At the moment, this includes Uncharted 4: A Thief's End, Doom, Overwatch and Homefront: The Revolution.

It's not clear whether this is a timed promotion or something Amazon will enforce indefinitely. The move will, in all likelihood, convert a few customers into Prime subscribers, however it could also aggravate people that can't afford, or would otherwise have no interest in the service. Amazon might be big, but it's not the only place that sells video games -- digital stores like Steam, for instance, are growing in popularity. Amazon is, therefore, risking its market dominance and its customers' loyalty.