Your theory regarding his man-management of Tevez is one I've been mulling around recently.
Of course, being someone who is actually a bit of a fan of Mancini means I'm coming at it from a different angle than others but maybe this is just Mancini's man-management style on the whole. He wants players pumped up to the max and sent on the pitch like coiled springs.
Many were pulling their hair out on Sunday as AJ warmed up for the bst part of an hour and they wanted him on much earlier. You don't have to believe me, but I did actually say to those around me at the time that I thought Mancini might be winding AJ intentionally, making him think he was going to be on the pitch any minute only to release him with 20 minutes to go.
A dangerous game as you might lose a player like Ade by doing that, he seems to know what makes AJ tick though because within 3 minutes he'd won us the game.
Just a theory.