If you think you use a lot of energy moving a weight a relatively short distance, well you need to think again. Think about it, if you bench 300lbs for 10 reps, you move 300lbs about 10-15 metres depending on you're range of motion, length of arm etc. I'm sure some of you smart people could work out the amount of energy needed to do that
Plus for most people in an hours weight lifting, you probably spend more time resting than actually doing exercise. Even the biggest rugby players probably don't burn much more than 1000-1100 calories a match and you think lifting a few weights while spending most of the time resting is going to burn the same amount of energy as this...