I would have to agree with you. Besides we touch more packages than the loaders do anyway. I average about 1200 an hour and I'm not the only one. Believe it or not I actually put on weight after I started. I used to weigh 195 lbs and now weigh 216 lbs.
EDIT: And it ain't fat. Thats muscle. So don't say I need more work to do. I got enough as it is. lol!!
Yes unloading and loading trailers is more physically demanding than pre-loading by far. At 24 hours fitness I burn 1600 calories in two hours on the treadmills and elliptical trainers and unloading seems much harder that's why I think people are burning more calories than they think.