PM is a team function, that of (in a nutshell) managing and tracking resources and tasks. It's also a field of study, and optionally a job title. At the level

PM is a team function, that of (in a nutshell) managing and tracking resources and tasks. It's also a field of study, and optionally a job title. At the level of abstraction of PM, software is exactly analogous to building skyscrapers, building a rocket, producing a theatre production or capping deepwater horizon. You are right that there is not just one way to organise a project. However, if the project is being organised at all, at least one person is doing project management. It's just that the acting PM(s) may not be formally trained it in, or have "PM" as their job title. That's fine.