This is interesting. I am surprised that amazon spends only $55 extra a year on shipping per prime user. This past month alone I've received ~30 packages, all 2 day free shipping from amazon prime. This included some very large objects like a rowing machine, and some small items like a ream of paper. Last year I had a 3'x3'x2' next day aired for 4 dollars in time for Christmas. If I were to try shipping these items the cost would be in the $300-$400 dollar range (for one month).

It's easy to think of something I need, hit amazon, select prime eligible, and buy in a matter of 3 clicks...No worry about cost or when it will be at my door.

Amazon must have a pretty good deal going with UPS (& FedEx for next day air).