Almost all commercial software licenses include costs associated with maintenance on the license and support of the software. Maintenance is what's required to keep software updated to the latest version and get patch updates. Support is what's generally required for asking questions and getting SLAs on bug reports and fixes to issues. In commercially licensed software, these are often combined into a single line item, "Maintenance and Support".
With OpenNMS, we've separated the notion of maintenance and support whereby you can get maintenance without paying for support. This gives you access to the private repositories for the software where you'll get all updates to the software. Support, which requires maintenance, is an additional set of offerings providing support at various levels and features.