It might be because of the selection of websites I visit. But all of the few times I can remember that I've seen somebody complain about their freedom of speech in web forums, there's been a good reason to shut them up.
[Edit]
Oh, I just remembered one person that got banned from Dimension3D for his posts where he insisted that there won't be a 3dfx chip in Dreamcast...
Maybe that one was a bit too much cencorship. But on the other hand, I believe it became a bit nasty in that thread after he got slammed for his absurd idea. Mud slinging in both directions, and it was probably easiest to ban the mud slinger that insisted on such a strange idea.
I don't think any posts were deleted or modified though, so it was probably meant just as a peace keeping operation.