Ive noticed the same thing. Just this year I arrowed a 6 point who was quartering away. The shot went through the liver, diaphram,right lung, and entered the left lung and stuck behind the shoulder blade. He ran 50 yards and piled up. I saw it all so I didnt have to trail him, but when I went back to pic up a vane that came off, I noticed there was no blood at all. When I field dressed him, there was little blood on him or the ground, but his abdomine and thorax was full. He had lots of internal bleeding, but not much came out.