Well, to be fair, people do say things like that about people who are robbed, things like "Oh you shouldn't have been in that part of town" or "You shouldn't have left your blinds open so the thief could see your computer", etc.
The problem is, and here's where I think things get tricky, is that it's one thing to talk to someone about common sense and say, "Hey, here's some decent tips to prevent *insert crime*" and another to tell a woman who has just been violently raped that she was asking for it.
THAT'S rape culture and it's sick and it's wrong. Wrong on so many levels. Because while you can say, here's some common sense tips about avoiding bad situations RAPE HAPPENS TO ALL KINDS OF PEOPLE. It doesn't matter what they were wearing. It doesn't matter if they are skinny or fat. It doesn't matter if they had on a short skirt. It doesn't matter and people who try to make it the victims fault are only encouraging a system that tells rapists that they didn't really do anything wrong.