It's not necessarily that they're angry with you, it's just that sorry doesn't make the pain go away. How about this scenario: a person runs over your dog and kills it. They say they're sorry. You understand that it was an accident, but you still feel devastated that the dog is gone. Too often, people think saying "I'm sorry" means you can go right back to how you were before the event. Often, that's impossible and you have a right to work through your grief even if what happened to you was an accident. But as you said, it shouldn't apply to clumsiness.