It appears to be a standard practice of the current marketplace to tempt gamers with exclusive preorder bonuses. We will offer you this spiffy gun if you preorder with our store! Get an exclusive skin with that store to show off your nerd! What is not standard is a company releasing those previously exclusive offers to the public at some point down the road.
Coinciding with the release of Batman: Arkham Asylum's Game of the Year edition for North America, Rocksteady has put up on the Marketplace two previously exclusive preorder maps. Those that purchased the collector's edition are familiar with the Crime Alley Challenge Map and those that preordered with GameStop received a code of the Dem Bones Challenge Map.
Each map is now available for purchase at 240 MSP a pop. That is 480 MSP for the dynamic duo, if you have trouble with your math.
This writer is not sure if they help with those pesky combat challenge and predator challenge achievements, but he is sure that someone with slightly more knowledge than he will let the faithful readers know in the comments thread.
To the Batcave!