Aren't there some stores that don't even take pre-orders? I think the Walmart around here doesn't even do pre orders and I'm sure I could walk in there that night at midnight and get one if I wanted to.
Any time I get a midnight release that's what I do and they always have plenty of copies of the most in demand games without me having ever pre ordered one. Most recently did it for GTA 5 and walked in at like 3 AM after the bar all hammered and they still had a ton of copies.
I thought all Wal-Marts were doing the pre-order thing and if they aren't then you're right. If they are though you won't be able to get one if they have all the pre-orders gone. I know when I got the Wii-U (for my nephew) they only had the people who pre-ordered them in stock. Everyone else was sh*t out of luck until the next supply which was a month later.