Oh, and there's this too: "Generally, when you run an IP addresses (past and present) through a search engine, it defaults to the largest town within a certain radius, thus preserving some sense of anonymity. What is being broadcasted on lj, however, is much more specific.

In one instance I entered an IP address from location x into a search engine and it showed my location to be ~20miles from x. LJ reported my location to be ~5miles from location x. (And, incidentally, the town lj announces is not even shown on some road maps.)"

So it was being much, much more specific than IP lookup.