Why some ISPs turn against their own customers

With the recent announcement that Britain's largest cable Internet Service Provider Virgin Media will start warning its customers, or better the part they suspect to download files without having the proper rights to do so, that they will face prosecution if they do not stop the behavior. Virgin Media calls it educating their customers during a ten week trial campaign but their letters will apparently be accompanied by letters from the British Phonographic Industry that threatens disconnection and court appearance.

Now the interesting question that arises is why they would want to educate their customers. My first assumption would be that they, as a cable provider, want to reduce the average bandwidth usage of their customers in an effort to maximize the profits from their infrastructure. Usually filesharers have a much higher bandwidth demand than the usual Internet user with the exception of video portal junkies maybe.

Reducing the amount of filesharers that are their customers would definitely reduce the bandwidth bill of the ISP. Cable is a shared connection as well which could increase the speed of all customers as well.

The interesting question will be how they will pick the customers that will receive the warnings. Will they actively monitor P2P networks, will they only react when the BPI sends them a list, will they verify those lists ? What about false positives ? Someone who is download music from Jamendo using the Bittorrent protocol. Will he receive a warning as well ? What about secure Usenet connections ? IRC, FTP, file hosts. How the hell will they be able to determine that a file that is being transferred is indeed a copyright violation ? Filenames alone are without doubt not the safest way of determining that. So, how will they do that ?

My second assumption would be that Virgin Media could have some ties with the BPI or a company that is a member of the BPI. I really do not have enough time to research this so if anyone could help me out it would be appreciated.