I believe the movie companies especially are having a big push on the ISP's and are threatening them to bring their users into line or they will get tough on them. This seems to be just another plan from them to try and curb the movie torrents (some hope) so much so that a few of the ISP's are taking the threats of law suits seriously and sh#tting themselves.
I know of at least 5 ISP's in the UK who have been recently sending out letters like the one you have mentioned to some of their customers just to prove that they were taking it seriously.
As jay has said the only real thing they are bothered about is bandwidth hogs. There are some ISP's who try to block or limit your speed if they are aware that you are downloading from torrent sites but some torrent apps have ways to encounter that.
uTorrent for example has a facility that you can enable encryption on it to mask it from them.
I do not know how effective it is though.