I don't recall Parallels announcing the end of life for Plesk on CentOS 3. Plesk 8.6.0 was released for RHEL 3, but not for CentOS 3. RHEL and CentOS are binary compatible, CentOS is just a rebuild of RHEL sources with different branding. I can understand Parallels dropping support for older operating systems, but dropping support with announcing it and still supporting a practically identical OS doesn't make a lot of sense to me.