There is definitely merit to the idea that, for many individuals, an incentivized network will be more beneficial. Over time, those individuals would naturally move towards those networks.
I suppose that my resistance to the idea of "all centralized services will eventually fail" is that I think centralization has many benefits, along with the downsides. In my mind, centralized and decentralized networks will co-exist - the same way that Snapchat became popular without destroying Facebook, I think that a blockchain service can become popular without fully disrupting the existent networks.
Well, i do think they will fail, not co-exist, because they have a business model that will be disrupted by blockchains, and all they proven over time is that they care first and second about money...
They should mutate a lot to survive, which i find hard they could do... I actually feel they are getting as much as they can from these networks now, as they know they wont last forever...
But again, this is all speculation of course, no one cant really know how the future will look like! ;)