This stat is skewed by the default instance on things like EC2 being Ubuntu or Debian (should note that EC2 is built on RHEL/CentOS). There's an awful lot of people's blogs and one-off websites running on Ubuntu or Debian, sure. Those aren't really "business" use cases.

Also that stat is only measuring "websites". As far as my company goes, the vast majority of our servers are not internet facing, I'm sure this is similar elsewhere.