Funny... OUR university group has standardized on RHEL, almost solely because of its aggressive approach to security updates.
As an old(er) Unix maven said to me, some twenty years ago, "Once you've secured your network against the Bad Guys on the outside, you can begin to defend it against those on the *inside*."
Some things haven't changed. The bulk of those probing and banging on our systems are this university's own students.
Yup, we run RHEL/5.5, and we're quite happy when RedHat pushes out yet-another security update.