Open Question: How does burning calories work?

Alright, so I started exercising today to go with my dieting. Now my question is, would a person who is heavier, and doing the same exercising as a person with a lower body weight burn the same amount of calories? I weight 280 lbs, walked on the elliptical machine for 20 minutes (for me just starting, this was alot :-\ ) and according the the machine i burned 165 calories. Now I have 2