My opinion about games' depth buffer

Some of the game's depth buffer is not open by default or not exist, but we can try to find it out in the game graphic options, turn off some graphic options or modify them may open the depth buffer, such as Call of Duty 2-4-5-6,all they need to turn of AA, Call of Duty 8,you have to set the “Image Quality” to “Native”; Assassin's Creed 2, you have to turn off “POST-EFFECTS”, but the protagonist and NPC and part of the buildings don’t have deep buffer, the Medal of Honor Airborne only the protagonist has deep buffer.

Do the Nvidia Control Panel influence the detection?

And are any of you capable of accessing any Telltale Games depth buffer?