To me, the biggest difference, and where all this "play tight" advice comes from, is that in a cash game, you do not need to take risks quite like you need to do in a tournament.

You have to take more risks in a tournament because if you don't, your money will disappear to blinds. In a cash game, you don't HAVE to take risks, and its often smarter not to (as there's nothing forcing you to do so like in a tournament).