"Over the course of a project, development teams do change and evolve from time-to-time," a 2K spokesperson told Joystiq. "While we can confirm that Martin Slater is no longer with the studio, there have been no changes to the way in which XCOM is being developed. The project continues to involve strong collaboration between our California and Australia locations and continues to be led by creative director Jonathan Pelling, a longstanding member of the talented team that worked on BioShock, BioShock 2, Freedom Force and Tribes."
While Slater's departure may not have caused changes in the way, or the process, that XCOM is being developed, that doesn't mean the game itself hasn't undergone changes since we saw it last, at E3 2010. We'll know for sure the next time we get our hands on the title. Probably E3 this year, right 2K?