I don't believe that's true. Can you cite one service that does this?
The TwitPic debacle recently—TwitPic changed their TOS to state that TwitPic could sell their users' pictures without authorization from or revenue sharing with, said user. So, TwitPic?
TwitPic doesn't strip your copyright. Their TOS states that you grant them the right to sell the image uploaded to them, but you still hold the original copyright. It was clearly described in the linked article.
I think the question was whether there were sites which stripped you of your copyright privileges, not of your copyright. I've argued elsewhere in the thread that these services cannot strip your copyright. However, if you give a license to a website to profit from your content, I think we can agree that the website stripped you from your copyright privileges (at least a big part of them).