Troll seems a little harsh for this comment. I am a die hard Amazon Prime user but you will find that the identical item that ships without prime is often $3-4 cheaper before shipping and about the same with. The difference though is that Prime is 2 day and the alternative is UPS ground or worse. So no, it isn't free, it is premium shipping discounted but that hardly reads as well on the advert. It also doesn't scale with size. All Prime items ship at a flat rate where UPS ground has variables like weight, size and distance.
The discover card comment is a bit troll-ish but it is probably the least used of the 4 big names out there. However, because I am a cheapskate I know that people on deal websites love discover for the 5% cash back which I think is the best in the industry. Also Costco used to only accept Discover (now AMEX). I'm no shill, i don't even have a discover card.