This emphasis may not be practical. Part of Red Hat's and Novell's reluctance to focus solely on the desktop is based on their own failure to sell distributions commercially, and, in the last year, Canonical has appeared increasingly desperate in it efforts to build a desktop-centered business. But, in the absence of strong rivals, for better or worse Ubuntu has become a main influence on thought about the free desktop.
It helps, too, that in former space-tourist Mark Shuttleworth, Canonical/Ubuntu has a famous representative with some charisma and considerable intellect. Shuttleworth has frequently been accused of egotism, but, to the extent that the charge is true, he is reminiscent of other free and open source software leaders such as Richard Stallman or Linus Torvalds.
Although often criticized, his is a style of leadership that the community understands, and helps to ensure that he has an audience -- especially in the absence of any rival advocates for the desktop.
At any rate, Ubuntu has been an advocate for improvement in the desktop from the beginning. If its name and its original slogan, "Linux for Human Beings," made that position very clear, so, too did its enhancements and tinkering. However, its contributions have been obscured because they have been released one or two at a time. Also, of course, few users both to go back and see what was done in earlier releases.
However, if my memories are correct, Ubuntu can claim a long string of firsts on the desktop. I believe that it was first major distribution to place the menu at the top left, where the eye falls on it first, instead of imitating Windows and placing it on the bottom left. Ubuntu was certainly the first to make tools for switching to multiple keyboards part of the standard installation -- or to add the fonts needed to use different layouts.
More recently, Ubuntu has incorporated more detailed help into the shell and into desktop applications. It has also introduced tools for managing software sources and updates as well as (in a triumph of pragmatism over ideology) restricted drivers. Once you start tallying, the list of Ubuntu's innovations quickly becomes a long one.
Just as important, behind these practical improvement has been Shuttleworth's constant discussions of interfaces and usability. You might think that Shuttleworth's challenge a couple of years ago to equal or outstrip Apple tinged was by jingoism or that his enthusiasm for Ubuntu's latest color scheme makes too much out of too little -- and, at times, I would have to agree with you.
Yet the point is that, by talking about usability and interfaces, then backing up the talk with concrete options, Shuttleworth and Ubuntu have made the free software community aware of these issues in a way that it had not been before.
Admittedly, some of the ideas implemented by Ubuntu have been more successful than others. The verdict on the shift of the title bar buttons to the left is still undecided.
Nor has GNOME accepted Ubuntu's modifications of the notification system -- although, significantly, Ubuntu's efforts seem to have encouraged GNOME to do its own overhaul on notifications.
Even KDE has been working on its notifications -- which, considering that Ubuntu uses GNOME as its default desktop and pays the most attention to it, shows just how far-reaching Shuttleworth's and Ubuntu's influence has been.
Whether Canonical and Ubuntu will continue to contribute to the free desktop in the same way is uncertain. The change in default colors early in 2010 seems to have symbolized a partial change in goals as well, a move away from innovation and towards ways of increasing profitability. You might even observe a sense of desperation in this change, as Canonical struggles to succeed with a desktop-centered business plan that has worked for no other company.
Yet even if Canonical/Ubuntu should switch directions or fail financially, that might not matter except sentimentally. Ubuntu has already made the desktop and usability part of the free software agenda in a way that they simply were not before -- and that may be a contribution more significant that the number of patches it contributes to the kernel or to GNOME.