Ok, so I took a closer look at XTube.
Very first video I look at is by this user:
http://www.xtube.com/user_videos.php?u=kameo20
I have no idea whether he's a webmaster or not, but none of the watermarked videos seem to have links going to sites by the programs owning the sites in the watermarks. Most videos seem to have been uploaded a full year ago and have thousands of views, so obviously, they're there to stay.
Somehow, I don't think users like this are an exception...