The fact is that there are rules. All projects must follow the Eclipse Development Process and conform to the Eclipse IP Policy (and engage in the IP Due Diligence Process).
It is the responsibility of the PMC to establish requirements, coordinate plans, etc. The PMC absolutely can set themes and priorities for releases, determine how projects fit together, etc. (the PMC should set themes and priorities in consultation with the project teams and build concensus, but ultimately has the power to impose). The PMC absolutely plays a role in making sure that all of the projects play well together. As others have suggested, for this to work, anarchy isn't an option.
The Specification Committee will decide how specifications get developed. Community input is, of course, welcome, but there are factors beyond simple democracy at work. There are, for example, legal responsibilities that need to be taken into consideration, and--ultimately--these specification aren't going to be of much use if the companies that build implementations based on the specs can't or won't implement them. The specification process needs to consider these (and other) factors.
It may look like open source projects (in general, not just at the Eclipse Foundation) are run by the committers in a bottom-up sort of way. And this is, to a very large extent true. However, there are many influences and controls. The spec committee will decide what specifications get accepted as official specifications; the projects providing the specifications, APIs, reference implementations, and TCKs need to work together; the PMC must approve releases, new committers, and new project leads; the companies that implement the specifications need to actually want to implement the specifications; and consumers need to actually be able to deploy applications using the technology.
Of course, all of the stakeholders are totally interrelated (there is a lot of overlap amoung project teams, the PMC, the spec committee, etc.). There's no us-vs-them, here. We're all just us.
Requiring that all project leads be elected isn't a priority, AFAIK.
Wayne