That's incorrect you can potentially need a licence for Amazon. It all depends on what you are watching on Amazon. Most of it doesn't require a licence but some of it does.
From the TV Licence site:
Subscription channels like Netflix, Amazon Prime/Instant Video and Now TV are television services that are normally paid for on a monthly basis via cable, satellite or the internet. ... But you don't need a TV Licence to watch on demand programmes (other than those on BBC iPlayer) on paid-for subscription channels.