It used to be that ordering household items from Amazon Prime meant stocking up. Many brick and mortar-resistant shoppers relished 48 rolls of toilet paper or 24 cans of cat food arriving at their address in two short days. Until recently, to protect Amazon’s retail margins, Amazon has made it difficult to purchase a single item in the $1-$5 range and also get fast and free shipping – items like a stick of deodorant, a make-up brush or a tube of toothpaste. In September, analysts at Edgewater Research started noticing that Amazon had disabled its add-on program, the system Amazon...