The employee evidently misunderstood regarding the discount when it came to exchanging the game.
It matters not who recieved the discount only that she was doing an even exchange.

I am sure by the time your wife got to the store the manager was overwhelmed with returns, exhanges and such so although his gruff "oh, just give it to her" response was a bit rude she still recieved her exchange.

Granted employees and management should be smiley and appear happy to serve all their customers. I am sure had this been a not so hectic time such as after Christmas the attitudes would have been less severe.

As for an apology I personally think your wife does not deserve one, but should they give it then I hope that makes YOU happy as you seem to be more upset about this incident than she. Otherwise she should have been the one writing this letter.