I think for people that cancel an account it would be easier to argue that they should possibly delete the customer info but I think there is still room for a company to be able to show reason why the keep it.
I do not know if equal waiting is given for each point covered by the DPA and feel that there is probably more emphasis placed on companies using the information in the way intended, ensuring it is secure (as far as they reasonably can), not releasing to others without permission etc.
The part regarding keeping longer than required is a more open ended point as it is easier to show that you have a need to keep it for a specified period as long as you treat it in the proper way and give the individual access to what you hold. But again this would need a case to be raised by the ICO to determine what their opinion of reasonable duration is in each case.

David,

You do have the right to request what information is held by plusnet about you...why don't you request it and actually find out....