Time hasn't stopped games such as Call of Duty Modern Warfare 2 and 3 from being released on the Mac years after their Windows debuts.
Two simple reasons for the lack of the titles mentioned in this thread are 1) Bethesda/Zenimax doesn't want to hand over the license to outside firms and/or 2) limitations of the game engine make it extremely difficult, if not impossible to port to OS X. I would say 2 is the far more likely scenario.