"Many people ask us why not use Debian-based systems such as Debian or Ubuntu server. We do support these if there is no other choice, but in our experience, they are not nearly as stable or trouble-free as RHEL/CentOS."

So while they do have "less experience" they do have ongoing experience with Debian or Ubuntu. They say. We don't know what that means it could mean 1 machine per year or it could mean 10 per month.

Now if they hadn't needed to support essentially any Debian/Ubuntu that might mean they are stale in that area. So without qualification of their exact experience "how often" it is really hard to tell the bias in that statement wouldn't you agree?