As seen in this topic: http://arduino.cc/forum/index.php/topic,110821.0.html, a user attempted to use the Mouse and Keyboard Libraries with an Uno. I suspect this won't be the last time.
Even those the Reference Home page says these libraries are Leonardo Specific, it may be a good idea to include that comment on each of the pages for the methods. That's where people are more likely to spend time reading and trying to understand why something doesn't work.