If it was called Call of Duty; Cliffs of Dover...they could be sued. I don't think they're going to sue anybody over the "unofficial" abbreviation "COD" developed and used by users.
Official name is Call of Duty not "COD"
Besides I don't think Call of Duty guys are too worried about the niche flight sim market. They've got bigger fish to fry with BF 3, Crysis 2 and countless other FPS clones to contend with.
