This has happened to me more times than I could count (well I could count them because of the way that I track my games, but thats neither here nor there). There are games it bothers me with and I will ask for a sealed one and if they have no others, I say thanks but no and walk out. I'm not going to be stunned that my local GS only got in one copy of Princess Debut for the DS, and that I'm buying sed copy and that the case has been opened. It's just the fact of life for games that are niche small titles and ones that have been on the shelves for a long time (like Oblivion).
What I don't get is that you said you looked online and it was going to take 2 weeks for the game to show up. Where is this the case? I check both Amazon and GameStop and they both currently have PS3, PC and 360 copies available for sale at 29 a pop, new and would ship in 24 hours. Heck, if you ordered Amazon, you'd have not even paid shipping if you chose Saver shipping and it would probably only show up a few days after a faster paid for method not to mention you'd have paid no sales tax either.
I can perfectly understand the desire to have a game now, I get that way any number of times a year. Especially if you arn't buying all that many in the first place due to your financial situation, but I guess i'm not feeling all that bad for you because you still chose to pull the trigger at the end. Their policy of displaying the games they have in stock forces them to gut a copy, its just how it is.