I wonder if we won't get a copyright problem if the images are
replaced... And even if not, shouldn't we show respect for the
Obviously not - the entire thing is under the GNU Free documentation License. The original images were taken from Astronomy picture of the Day, and checking the "About" page, I see they were not released under any kind of free license; some of them may be copyrighted. If anything, replacing the images will make the doc more free. As for my own pictures, I figure if I add them to the documentation they fall under the GNU FDL.
Anther reason for taking the time to replace all of them was that I wanted all the screenshots to have a similar theme (clearlooks, which I believe is the Gnome 2.x default) and I had to replace at least some because the interface has changed.
As for respect, I have all respect to Carol Spears who invested her time and effort to write the original tutorials, and I kept the credit in the introduction. But while it is natural for tutorials on personal website to maintain a casual tone and have tangential interests such as astronomy feature in the tutorials, I believe official documentation should be more professional. These are, after all, quick tutorials for those who don't want to read the entire manual to get some small task done; I tried to make it as short and to the point as possible.