Agreed but if someone had the balls to compete with either of those, there's nothing stopping them. Zappos has shown that the way to beat Amazon is not by compe

Agreed but if someone had the balls to compete with either of those, there's nothing stopping them. Zappos has shown that the way to beat Amazon is not by competing on price. Groupon is an advertising company, which knows how to leverage technology. It's not like they invented email marketing. They just know how to use it damn well. When you are selling other people's stuff, the only limitation is how much stuff other people are selling, which is apparently infinite. See Google.