I don't think this is unique to Amazon. Because that transaction costs have become so low(and becoming lower), almost everything is out-sourceable, and naturally in many fields there are advantages to scale, and network effects - common characteristics of infrastructure - a lot of business tasks are becoming infrastructure-like.
Amazon maybe saw it before others. But also, they are in a position that enables them to gradually take more parts of that emerging infrastructure, by owning the customer.
But let's say every stable, low-risk, repeatable task is outsourced outside of businesses into a few large corps. Can new businesses live in that environment? And how will competition look like ?
A business which owns businesses.
Amazon is taking the concept to the extreme in that it starts its businesses.