If I had bought the game from a store that did this, I'd be returning it for a refund. Selling an opened game as new isn't right and isn't what the customers expected. I've read that Gamestop has since stopped doing this and is recalling the games. They should have done that in the first place, instead of taking the coupons out. I can understand not wanting to advertise for one's competitor, but removing content from a sealed package isn't the way to handle it.
And plus, just imagine how many of these coupons will go "missing" because some employee decides they want a free copy of the game.