The calorie burn is higher because you normally move your arms as well as your legs, generating more calories burned for the same effort
Moving the arms on an elliptical doen't increase the number of calories burned that much.
Keep in mind that the machine is only going to give you an estimate.
The machines do only give you and estimate. Usually, it an overestimate.
No surprise: Cardio machines overestimate your calorie burn
http://www.consumersearch.com/blog/no-s ... lorie-burn
That is why you hear fat people proudly talking about how they burned 1000 during their workout. It ain't happening.
Ellipticals appear to give and even higher overestimation than treadmills and bikes.
Some of this probably has to do incorrect calculations in the design of the formula place in the machine to measure calorie expenditure.
I also suspect that the manufacturers themselves purposely exaggerate to sell them.
It similar to a dress manufacturer labeling a womans size 6 as a size 4. Women were buying the dress brand because they could tout they were were a size 4. The manufacturer downsized all the dresses sizes like that.
Same thing with food now. They keep the price the same but make the container smaller.