I saw some on ebay as well, and they indicated that the Marineland canisters only begun selling in February '07. So they may not have updated their web site, or your computer is still pulling from an archived form of the site.
Aquarium Pharmaceuticals (Rena) took a while to update their site to include the XP4 as well.
75g FW Planted Community; 55g African Cichlid
29g Biocube SW Reef;12g AP Mantis Shrimp/Brittle Star
2 Cats, 2 Dogs, 5 Turtles