While I’m not really sure I understand the versioning of HBase, it looks like every minor release comes with a long list of bug fixes and improvements, the latest version released, HBase 0.20.4 featuring over 80. You can find a complete list ☞ here.
A Top-Level Project signifies that a Project’s community and products have been well-governed under the ASF’s meritocratic, consensus-driven process and principles. Whilst a project is developing within the Apache Incubator or as a sub-project of an existing TLP, it benefits from hands-on mentoring from other Apache contributors, as well as the Foundation’s widely-emulated process, stewardship, outreach, support, and community events.
"Becoming a Top-Level Project is a vote of confidence from the Foundation at-large, demonstrating a project has proven its ability to be properly self-governed," said ASF Chairman Jim Jagielski. "We are proud of our Committers’ dedication in building robust communities under the ASF process known as ‘The Apache Way’."