I understand your thesis
I expected to be able to say with complete confidence that the three games didn't really make a difference, and that they could have been swapped out with any other three games and sales wouldn't have been affected more than maybe a couple % points.
I think theres something to it though, not so much the tanks, but the shooting range and table hockey are a couple of games that probably inspired a lot of impulse purchases. They see the game with the Wiimote included, pick it up and see shooting range and table hockey on the back and the purchase is almost automatic.
Edit: except I just looked at the back of the case and table hockey isn't featured very prominently at all. In fact now I think pool and ping pong might have played a larger roll. Ping pong, Pool, and shooting range are all highlighted well on both the front and back of the case.
