Precisely......the storage-media costs alone would bankrupt most ISPs.

To give you an example, I've got a program here that can monitor traffic just connecting to/from my own machine (Ethereal, for anyone who's interested in trying the program out). If I set it to monitor for 60 seconds, it may pick up anything from 100 to 5,000 packets, depending on what I'm doing during those 60 seconds (browsing is quite low-load, gaming would be medium-ish, P2P would be high-load).

So, imagine those 5,000 packets displaying ALL packet-information, assuming you're talking about 1k of info for each packet, there's 5MB of stored information for one computer on one network for just 60 seconds of information. So, extend that 60 seconds to an entire day, and you have a touch over 7GB of information, for one computer on one network. Extend that to the 12 months the above claims the records need to be stored for, and you have roughly 2.5TB of storage required. Now, that's just one computer on one network. Assume (very very roughly, for example's purposes) that an ISP has 100,000 customers, and that (again, for example's sake) they all use a uniform amount of bandwidth over those 12 months. That now makes 250,000 TB of data that needs to be stored.

So, using current prices and assuming a hefty ISP discount for buying in bulk, the cost of buying enough suitable media (for this example, I'm using Sony S-AIT 500GB tapes, quite widely used) to store this information on would cost in the region of £50,000,000.

Seeing the point yet?