Leia a FAQ do Centos uma pergunta que tem a resposta:
Como o CentOS é diferente do Red Hat Enterprise Linux?
CentOS is a community project that is developed, maintained, and supported by and for its users and contributors. Red Hat Enterprise Linux is a subscription product that is developed, maintained, and supported by Red Hat for its subscribers.
While CentOS is derived from the Red Hat Enterprise Linux codebase, CentOS and Red Hat Enterprise Linux are distinguished by divergent build environments, QA processes, and, in some editions, different kernels and other open source components. For this reason, the CentOS binaries are not the same as the Red Hat Enterprise Linux binaries.
The two also have very different focuses. While CentOS delivers a distribution with strong community support, Red Hat Enterprise Linux provides a stable enterprise platform with a focus on security, reliability, and performance as well as hardware, software, and government certifications for production deployments. Red Hat also delivers training, and an entire support organization ready to fix problems and deliver future flexibility by getting features worked into new versions.
Once in use, the operating systems often diverge further, as users selectively install patches to address bugs and security vulnerabilities to maintain their respective installs. In addition, the CentOS Project maintains code repositories of software that are not part of the Red Hat Enterprise Linux codebase. This includes feature changes selected by the CentOS Project. These are available as extra/additional packages and environments for CentOS users.