Network-based business models have always tended toward monopoly (AT&T, ConEd, and Western Union, to name a few early US examples). The internet doesn't change this dynamic at all; rather, by providing the first (more or less) open network in history, it simply removed what used to be the greatest impediment to a networked business: the construction of the transmission network.

The internet hasn't "changed" economics, it's just enabled a specific type of business model.