A new post has appeared on RalphsValve's Twitter account, which indicates that the authors of the Call of Duty game series plan to stop releasing further parts on previous generation consoles. According to the author, this may happen after the release of Modern Warfare 2, as the recent release of the first part showed that the Infinity Ward engine is much better suited to the needs of studios than the iD Tech3 Engine.
Thus, Activision decided to completely transfer development to a new system. And this, in turn, leads to the refusal to release new parts of the shooter on the PS4 and Xbox One platforms, which, apparently, can no longer cope with Infinity Ward.
So far, we should take the insider's words as rumors, but usually RalphsValve's statements are confirmed by official news over time.