If you looked at volume of commits it might tell a different story - I'd imagine commits by contributor would follow a power law, so you might well have a project where 5% of the contributors made more than 50% of the commits, for example.

That's a non-sequitur. Are you trying to suggest a relationship between an open-source project with many contributors and a requirement to avoid building a complete platform? If so, could you provide an argument behind your statement?