Oh come on now. Cap is still trapped under the Arctic Ice at this current point in time if they're goinbg by that bit of continuity. He probably won't be rescued until the Avengers movie, with the Cap movie being placed during WWII. Now Tony, having all that money could be able to afford to give the U.S. military a little commission for that shield the military no doubt had found way back in the 40's when searching for Cap. It would say something about our disposable culture of today that a possession that once belonged to an icon back in the 40's is so meaningless today that it would be sold to the highest bidder, even if said bidder was Tony Stark.