That is probably a minimum specification so manufacturers of
No, 500mA is the maximum for USB according to the USB specification (versions 1 and 2, anyway, not sure about USB3).
USB spec says a device can have 100mA for "free", and can negotiate with the host for up to 500mA. In practice, many hosts will supply 500mA without negotiation. There are also other deviations from that spec, such as the Macs that provide 1A or more for charging iPads.
Powering a motor directly from an output on the arduino will kill the processor - maybe one output pin, maybe the whole IC. The maximum for a single pin is 40mA (that's on the original ATmega8, newer may be a bit higher but similar).
Keep trying to drive a motor from an output pin and you will kill your arduino, if you haven't already.
-j