It’s fun to see that Ubuntu’s design has actually been made on MacOSX with Photoshop. This applies to the default theme, but it looks like the CD cover and label artwork have also been made with Photoshop on OSX.
Here’s how the background was “fixed” after the discovery: the Photoshop signature has been wiped off the file. Amazing.
It looks like Ubuntu is all so a replacement for Windows or OSX that using Photoshop and Illustrator remains a common way to draw Ubuntu backgrounds.