well, anybody can set up a webshop (but only amazon got a dominant position), or some social network site where you can update your status etc (but only fb got dominant position).
Some companies will end up in dominant position, even though it looks easy for everybody. Brand recognition, and being early may be enough.
Amazon was on rocky ground for a long time. Through excellent ideas and diversification, Amazon seems to have pulled through. Not to forget that Amazon invented Kindle - a real product. And it sells real goods. Amazon has managed to drive most of the other online booksellers to the brink. It remains to be seen if those booksellers’ brick and mortar business will survive. Amazon is more of a retailer than anything else. It just does it better than anyone else. There is almost nothing that can’t be bought through Amazon. Their free shipping policy and their returns policy make them a dream for the consumer.
One other thing that Amazon has done is the customers’ rating of products. This is an educational service beyond compare. (Can you tell I am a big fan of Amazon?)
These other entities are nothing. They are air. They depend on the fad of the moment. Just ask AOL how quickly that can change.