First understand that PCLinuxOS is a "rolling update" distribution. Things are can change almost daily. When a new program or update is available, the packagers will update it and make it available. This is the same with security issues. When one is announced and a fix is published, the update is made available via the Synaptic update.
So to answer your specific question, there are security updates, it's just that they are part of the continuing development and update process.
By the way... the 2010 Release is "just around the corner".