In 2003 Matt Mullenweg and the team released version .07 of the open source WordPress project. From then until now it has, and will be (according to Matt) released in the GNU GPL. That means that the source code, and that of the themes is also released to the public under the GNU GPL.
Then, in version 0.07 one of the big benefits was a New Administration Interface. And it seems we have come full circle, with the new 3.0 version also touting a new and (much) improved administration interface.
Happy Birthday WordPress!