Halo 2 Vista & Shadowrun Combo

First Halo helped Crackdown get a ton of press and news by combining the beta with the game. Now Halo 2 is helping Shadowrun on Vista. According to an ars technica article a Circuit City ad lets gamers buy Halo 2 Vista for $40, then you get Shadowrun for free. This doesn't make any sense. How does a $50 game become free after being out for less than a month? I guess this is M$ way of pushing sales for Shadowrun on the PC side. Poor FASA studios.