It's one thing for the guy running a web server to keep logs for 18 months. That's probably easy given cheap disk and compression. But the web site host is not an ISP. They could be anybody, and they're probably not going to record logs if they have material they want to hide.
It would be impossible for an ISP to record all traffic though. I have a 100 Mbit/s connection to the internet now. Can they possible write a record to disk of every connection I make over HTTP? How about NNTP, SMTP, etc. Then, multiply that across tens of thousands of users at today's broadband speeds. It just can't be done!
For an analogy, have someone hop on a subway train and record in a notebook every time one person speaks to another person. Then, assume there are 200 people on each subway car, multiplied by 200 cars, multiplied by hundreds of cities... You'd exhaust the worlds paper supply in a week!
At best, they should be able to give a warrant to an ISP to record a specific IP address for a period of time just like a normal wire tap would happen.