You never know though. If a game programmer really wants to keep something secret, they can find a way to do it. I remember when star wars rogue squadron came out for the N64, before The Phantom Menace was in theaters, and it was like a year or two before anybody even knew that one of the fighters from the new movie was actually an unlockable ship in the game amidst all the other original trilogy ships. And infact, i think that the actual company was the one to release the code, since nobody came public with it.
So, i firmly believe in our ability to uncover stuff without any help from the cheat sites and magazines and companies and what not, but i also believe that there's always the possibility that we might miss a thing or two.