[suicideneil]

The ratings you see (if they are noted in the specs, not always), is the maximum the motor will pull (peak) at its maximum rated voltage. I know Neu list the maximum amps and wattage achievable, so that makes choosing batts and escs easier. Generally though, you only see high current spikes under acceleration, or any time there is a heavy load o the motor- landing jump at WOT for example (bad idea).

As for what limits the power, its in the design of the motor. Smaller motors pull less current, and the number of turns/winds (kv rating ultimately) effects its power output; a higher kv motor will pull more amps than a lower kv motor of the same design/size.