The timing couldn't of been worse, but we all got a mortgage to pay. That is how I see this jump to EA with a new studio.
It is possible that West and Zampella where looking into new places of employment, which I do not think can be considered a breach of contract like how looking at another women isn't considered cheating on your wife. The "look don't touch" policy. West and Zempella probably felt that their leaving from Infinity Ward, and subsequently Activision, was inevitable sooner or later and felt it necessary to find places that where willing to hire, without actually going to the company with full intentions to work there.
EA is probably one of few publishers out side of Activision that have the ability to draw up a contract, make a studio, and throw down the necessary copyrights and all that jazz in a short amount of time, as it is amazing what large sums of money can do. Also, it is amazing how proven talent, experience and qualifications can draw up a contract that demand certain things, like retaining independence and the like and thusly make the needed positions available without any problems. West and Zempella have proven themselves more than adequate in this industry and therefore have the ability to negotiate what they want, as EA has the resources to make all that happen quickly.
On the other hand, if West and Zempella where wheeling and dealing with EA while still employed at Infinity Ward than that can easily be considered as a breach of contract, as most companies will not allow an employee to work with the competition. Making a contract with a competitor would fall under this. This would be actually cheating on your wife with another women, to complete the metaphor. Thus making Activision in the right, in terms of breaching the contract. On the other claims of withholding pay and "interrogating" IW employees, that remains to be seen, and if these can be proved then Activision can be nabbed for creating a hostile work environment and stuff like that.
Either way, I am glad these two guys have found a place to push their creativity more freely. I look at what EA has been doing as of late, and they seem more then willing to launch new IPs (Dead Space, Mirror's Edge, ect), and support the creative flows that go into a game. It is true that EA was not much unlike what Activision is today, but EA saw the monster it had become and set to change that. Activsion has failed to see what it has become and with the way things are going, it may be a while until they make a turn around like EA, if they can make it to that point. Multi-million dollar franchises only goes so far until you milk it dry and no one cares for what you make any more. As in almost any industry, when you stop listening to the customer, you will lose the customer.