This might be the start of a mass exodus as two more have left Infinity Ward. Todd Alderman, lead designer and Francesco Gigliotti, lead software engineer have resigned
from the company. Kotaku has their current Linked In profiles showing they are former employees of IW.
I'm not a stranger to leaving a company after some issues that cropped up with other employees. While it can be hard to leave a company you're with for a long time, sometimes you have no choice and you have to do what's best for yourself. I wish Todd and Francesco best of luck and wouldn't be surprised if they turned up with the two other ex Infinity Ward folks in some new venture.