A lot of misinformation going around. I work at Wal-Mart too, as an overnight support manager (for those who know what that position is).
If your manager yells at you for ANYTHING, that is a problem with the manager, not a company problem. Use the open door policy, and if it happens often, make sure you are "yelled at" with a witness present.
Also, a LOT of people THINK they work hard, when they really don't.
Edit: it took me 3 years to get to my position from starting out as an unloader. I have basically been promoted once a year because I am a damn good worker. Ive seen others move up just as fast, non military.