I entered the exact title of some TV series and got no results at all from LW when you can get results from, say, e-donkey. Is it because of copyrights or something?

Also if you start searching for a specific video and enter the exact title you may get lots of results but it's impossible to download any. Bitzi tells you they have no bitprints for any of them (if you bother to check with many of them) when you know that they exist because they can be downloaded from e-donkey for instance, or a search from the Bitzi site turns out quite a number of results some of them are listed in the LimeWire search results and yet can't be downloaded (need new sources, it says)