Actually, amazon hasn't been very clear about whether or not physically lending a kindle is within their terms of service.
http://www.libraryjournal.com/article/CA6649814.html?rssid=1...
http://www.libraryjournal.com/article/CA6649814.html?rssid=1...
[1]http://www.apple.com/legal/itunes/us/terms.html#SERVICE Under Intellectual Property
So, I do not think this would get struck down quickly. I do doubt that studios would dare sue in this case, though. Under pressure from public opinion, laws can change very quickly, and such a change could see studios lose quite a few sources of income.