Im guessing the reason why is that the authors dont want their tool to be used to make a lot of money for someone else who plans to sell a screensaver.
My new
Multi Photo Quotes can be used to build and package your own screensavers and is free for non-commercial use.
Phil's idea is actually quite clever and i never thought of it

But i can see why Carol would want a PPT specific thing.. it might be possible to kludge together something which basically cleared the screen then launched the free powerpoint viewer to show a ppt, then killed the ppt viewer on user input.