That's the only business model as long as you ignore Automattic, Chef, CloudBees, Cloudera, Confluent, Databricks, DataStax, Gradle, Hashicorp, nginx, Puppet, RedHat, and many others.
Some of those companies make money by selling proprietary software. They are thus proprietary software companies, and bad examples of open source software business models.
What are good examples?
Red Hat. They work with the community upstream, and they open source all their stuff.