Up to recently, ISP felt that they had the same status as traditional telecommunication provider and were protected from prosecution for the traffic going through their network. It was then none of their business to police the information flowing through their network.
The situation became hazier when BT decided to deploy [cleanfeed](http://en.wikipedia.org/wiki/Cleanfeed_(content_blocking_system). Up to that point ISP had been transproxying web traffic in order to cache the web page requested and save on bandwidth cost but had never actively interfered with the data passing through their network.
More recently threat of legislation pushed by the IFPI, children protection lobby, and government (all ignoring that transproxying can be easily evaded) seems to be changing the landscape for ISP, which are now under increased pressure to police their traffic for the benefit of who can afford to lobby them.
Deploying large scale filtering/transproxying solution is expensive, and with little chance of seeing the cost paid the either the end user or the legislator, It is only natural for ISP to seek some kind of form or remuneration of the cost of deploying such possibly soon legally required solutions.
In that context it is not that strange to see the UK largest ISP sell their customer web traffic (not protect by any data protection law) to an organisation selling targeted advertising.
The most interesting part seems to be that even once ‘unsubscribed’ the traffic may still go through the advertiser ‘anomyser proxies’. One can only wonder if those proxies role will not block cookies from competitors giving Phorm a quasi monopoly for advertising in the UK.