I don't think you can take infrastructure seriously without a staging environment. For many companies that is fine - they don't have significant infrastructure to maintain (or just don't maintain the infrastructure they have).

I work on a team that maintains our database layer and the lack of a staging environment is incredibly painful. Every test has to be done in production and massive effort needs to be taken to proceed safely. With a staging environment you can be more aggressive and come up with a solid benchmark and test suite to gain confidence rather than having to data collect in prod