Plus there is foreknowledge when you know that a trap is there because you've already played the game.
But when all is said and done there is the notion that a CRPG should take into account the character's skill instead of a player's ability to play a game. It's a lot easier to stick to that principle when you're playing pen and paper RPGs and everything hangs on the roll of a die. In a videogame you often have the option to make up for a character's shortcomings with your own skill. Take Fallout New Vegas for instance, a character's skill is almost irrelevant compared to the player's ability to play a first person shooter which is why I like Alpha Protocol since the character's skill will severely impact your ability to aim.
Of course even when playing pen and paper you can get clues that do not come from the game. So in a computer game you can as the player notice something odd and suspect the presence of a trap but in a pen and paper game you may notice that the game master is spending a little more time than usual looking at his or her notes or that there is some die rolling happening on the other side of the screen.