It would be interesting to hear an insider story about the fall of AOL and Altavista.
It's clear that Google and Facebook are the problems and practically equivalent to the AOL walled garden.
I'm not sure that it would be impossible to disrupt them. What is lacking? Is it the fighting spirit?
The marketplace being global might not very much longer be the case. For example, the EU court of justice has ruled (again) that personally-identifiable info just can't be transferred to the US under the "safe harbor" doctrine. And hasn't Google pulled out of China because they were required to give data to the government which however they weren't willing to on matters of principle?