And neither is Debian (stable). But given that they're often used for the same purpose (servers), it's not that irrational to compare them. Having a larger, supported package selection (even if it's a bit old) may be a good thing, and relevant when you choose your distro.

For the record: I have no idea how the package selection compares between CentOS and Debian - I've been firmly in the Debian camp since forever, and stay there mostly for other reasons, of which laziness is the most important one.