1st of all it's not unfair or something if everyone hast the same possibilities.
Okay, it seems to be a little unrealistic, but who knows how many ghost are watching you in fromt of your pc at the moment.. and we all know (from movies) they can go through walls and stuff
..
Then this game is so fast, that even if u ..accidently.. spy someones position, until you are there, he will most likely be gone already.
And on the realistic modes, when it really becomes important, one usually stays dead until next round. So spying is no problem at all ...as long as 'dead ppl can't talk'.