Here we are at the start of 2016, when Prime membership costs $99 a year, and a new report from Consumer Intelligence Research Partners (CIRP) estimates that there are currently roughly 54 million Amazon Prime members in the U.S. Overall, 47% of the people who shop at Amazon are Prime members, the study says. For Amazon, the astonishing growth of Prime is a tremendous win-win. Amazon benefits doubly with Prime because 1) it collects annual subscription fees from tens of millions of consumers; and 2) subscribers tend to spend a disproportionately high amount of money with Amazon compared to non-members....