They say that Debian servers come from new servers, and many subsequentially change to Ubuntu. From the graph it's clear that CentOS and Debian is mostly steady, Ubuntu is on the rise and everything else is on the way down (in percentages of course).

I'm curious because I don't follow server distro updates often: what server-side stuff did Ubuntu improve on? I was under the impression that most of their gains were on new user experience as opposed to traditional administration.

This may seem like a stupid little thing, but I particularly love what they have done with GNU Screen, which is now called Byobu on Ubuntu.

https://help.ubuntu.com/community/Byobu

They have created Screen, and they have a lot of Cloud tools they've created based on Openstack. They also have some better default service configurations. [citation needed].

Canonical did not create screen; it is a GNU project that existed before Ubuntu ever did. They did, however, develop an extended, improved version of it (byobu).

It isn't really a "version" of screen. It is a bunch of scripts and wrappers using/around hooks that screen had built in (but hardly anyone ever knew existed).

It is a rather nice little set of basic improvements though.