Not to mention that Debian consistently supports "in-place" upgrades when moving between releases, minimizing admin time doing the upgrade, and actual server downtime. Whereas Ubuntu... I tried using it on a few servers, their complete lack of in-place support meant the servers had to be rebuilt from scratch on a near-yearly basis if we wanted the latest release. Just not feasible.
Not to mention: if you're not at least using configuration management by now, you're doing it wrong. Rebuilding a server should be a completely automatic process.
In fairness, RHEL/CentOS did not support in-place upgrades between major releases until RHEL/CentOS 7 (just released). Prior to 7, it was recommend to always do a fresh install.
