Seems as though talking to rival publishers may be the reason for IW firings...

If you take a look at this article, http://gameinformer.com/b/news/archive/2010/03/01/news-what-s-going-down-at-infinity-ward.aspx it says that they may have been fired because of discussions with rival gaming companies, thus breaching their contract with Activision. Well, there goes that mystery...