While I think the magnets probably have more to do with it (as others mentioned) it's also possible it has tighter brush springs. Tighter brush springs can increase torque, while losing a bit of efficiency and RPMs. If this is the case it could also contribute to what you are experiencing.

Brushless motors can behave the same way. Some brushless motors spin virtually completely smooth. With others you can feel the magnets creating resistance and they are harder to turn. Some motors (my new Castle/Neu motor is an example) will noticebly reduce the roll time of the car due to the magnets causing drag when not on the throttle.