Their other commonality is that they are "new markets". As the article indicated, monopolies do tend to spring up in new markets. In new markets, what to do to be successful is not immediately obvious, so the difference between competitors is much greater.
As markets mature, the differentiation between competitors lessens. Does that mean that the competition will increase? In the case of Amazon or Google, it should. However, it's possible that Amazon or Google will gain governmental barriers to competitors (they're big enough to buy congressmen), or quasi-governmental barriers (a-la Paypal) or strong arm barriers (a-la Standard Oil). Let's hope that they don't gain those barriers.
As markets mature, the differentiation between competitors lessens. Does that mean that the competition will increase? In the case of Amazon or Google, it should. However, it's possible that Amazon or Google will gain governmental barriers to competitors (they're big enough to buy congressmen), or quasi-governmental barriers (a-la Paypal) or strong arm barriers (a-la Standard Oil). Let's hope that they don't gain those barriers.