Because that's what these companies do, they put placeholders up to get pre-orders.

WoW expansion: http://www.amazon.com/World-Warcraft-Mists-Pandaria-Pc/dp/B0050SZBP6/ref=sr_1_1?s=videogames&ie=UTF8&qid=1320155589&sr=1-1

GTA V: http://www.amazon.com/Grand-Theft-Auto-V-Playstation-3/dp/B0050SXKU4/ref=sr_1_1?s=videogames&ie=UTF8&qid=1320155632&sr=1-1

etc.