Mantaining the logs and the continued logging of every download, page visited, time spent there, email in & out on all the clients that the ISP has, could result in an unreasonable burden. Should they be expected to retain it all for any serious length of time and of course where would they stow it? That gets expensive. They may backup email because of the potential future need, but the rest? I would guess, if the local cop shop has a specific interest, they may approach the ISP and have him retain those logs for review.
But where ever you go, doesn't your ISP log your IP address and keep logs by Law.