I always wonder how they gather they statistics, and to which extend we can trust the claims made.
Personnaly, I gather statistics on emule network, and porn films are not present on top50 most downloaded files.
TV shows sometimes appear, last month for example, in france, prison break was incredibly present in the top 50 with more than 15 episodes, but the most downloaded files, not surprisingly, seems to be the most marketized films...
If you want to check yourself :
http://www.emule-top50.com/