Sometimes the primarily responsible person isn't a developer on a given team. Especially at smaller firms, hats of responsibility are passed around to multiple members of the team, regardless of that member's particular talents/core competencies.

We call them project champions. I work in an agency model, so we have many clients who have many projects. The project champion usually knows the client, their wishes, etc - acts like a product owner (if you're familiar with the term from agile methods).