What's so different about locking bikes as opposed to locking cars (or houses or businesses)? It's just something you do. I'd be willing to wager that all the cars in the lot at my grocery store are locked.
You'd be hard pressed to ever find my car locked. I even leave the keys in it when I'm at work. But then again, it may be that I live in a fairly low-crime town that I don't feel the need to lock up. And yeah, there's been a number of times I've forgotten to lock the house up.