A lot of people have begun using the term ecosystem to describe these big platforms. That captures their decentralized, emergent character, but ecosystems do not have a central point of control. Apple decided to eliminate third party analytics between one release and the next. That doesn't happen in an ecosystem. The right analogy is a government.
If you accept the analogy of web services as governments, the example of Craigslist offers a couple of insights. First, it's possible to be fabulously profitable as a restrained government, but perhaps at the expense of top line revenue (or the government's share of total GDP). And second, that no web service is an island. Web services will compete with each other for the time and attention of their users and for investment from the private sector (applications developers), but they will do this in the context of their host government's who are also competing for tax revenues and private sector investment.