The data (and metadata) is definitely important. And yes the Sun is a singleton in our solar system. Closer to home, if anything goes wrong with the earth, (asteroid, LHC, some unknown weapons programme) we're all doomed, including all ecosystems on the planet (depending of course on the magnitude of the disaster). The field of global existential risks is devoted to asking such questions.
That being said, I would rather my work depends on the sun's or earth's continued existence, rather than on twitter's or facebook's or amazon's uptime/finances/goodwill. We should aim to remove SPOFs/SPOCs to the extent possible.
But ecosystems are not only biological they are also physical and the sun is a pretty good candidate for a singleton then isns't?
To me the defining factor is the flow and exchange of energy throughout the system. In digital ecosystems the data is what needs to flow.
The internet is obviously the mother of all digital ecosystems but it is also restrictive (firewalls etc) which keeps data from flowing.