Having gone over the motions that Activision threw into their suit (they're up on Joystiq) and snuck at peek at the email referenced above, either Activision is throwing whatever it has at the wall to see what sticks or it's been spending a while gathering evidence against EA before widening their suit. I'm leaning towards the latter, since Activision isn't just saying, "Oh, EA tried to poach our talent."; they're saying, "EA worked with Infinity Ward to kill Call of Duty."
Heh. What's funny is that presumably this all took place back in July 2009, eight months before Activision kicked Zampella and West out. Hey, whattaya know? Bob Kotick was justified in the firing and it's all thanks to confidential emails discovered by Activision when they demanded records from EA. Except...hold on...that map pack was announced in March 2010...after the heads of Infinity Ward were already fired...and the whole conspiracy is supposed to have started five months before the actual game came out? So if Infinity Ward really had planned on screwing Activision, they were in a position to ensure the game didn't reach market at all or at least reached it in a condition that would wreck any hope Activision had of making back its investment.
Your addendum doesn't pass the smell test, Activision, and I'm pretty sure that if you don't find iron clad proof that Infinity Ward wanted to rip you off with EA's help, you be fucked. And it's going to take a good deal more than an EA director saying Vince Zampella "owed him a favour" in an internal email.
The final insult? That email is dated the day Zampella and West got fired. Hmmm. Now why would EA executives be talking about two executives of Infinity Ward the day they got fired? Oh yeah! It was in the news!