The Bog Lurker was indeed one of those special rare spawns for Outland! They are actually quite rare, they have a respawn timer of 0.5-2 hours, and only a few (2-3) of all of that list would be up at any given time across the entire Outland! So when you'd kill one, usually a completely different one would spawn somewhere else. They dropped a very particular rare BoE item, usually associated with them directly by name, with very decent stats. Once Wrath of the Lich King came out, they did the same thing there as well, and also Achievements were introduced, so then players wanted to hunt every single one of those for the final achievement of each location series. And I can easily see how the Bog Lurker could be the final elusive Outland rare for someone to have to hunt him for days =D And you just ran into him without even looking for him specifically!
I'm not sure how it works with Chromie Time, but when you get to Cata I'd suggest ignoring all the revamped vanilla zones and instead focusing on the new zones that Cata added (Mount Hyjal, Vash'jir, Deepholm, Uldum, Twilight Highlands)
