"Because we said so"
I recently asked why you can't do this:
Why can't videos be downloaded, a la Google Video? If the site is filled with 'non-copyright' material, why are we still barred to watching it here?
And the response I got was:
Unfortunately we cannot counsel you on legal copyright matters. What you might want to do is to read up on the 'DMCA' which discusses the laws for digital media. Here's a link to an online version of this:
YouTube does not allow pornographic, obscene, or copyright material to be uploaded. Of course, if you are the OWNER of the video, it is welcomed with open, er, arms! I hope this has helped, and thanks for the email!