I'm not aware of any spec requirements for overcurrent protection on the host ports (devices have strict power behavior per spec), though they may be there.
I am aware, however, of countless USB host designs that simply put a 5v regulator rail on the power line and could probably be induced to overheat by a misbehaving device.
It's definitely in the USB 1.1 spec, (with some verbiage that excessive current draw on one port is not allowed to affect other ports) though they may have relaxed it later. I have several old Belkin hubs that will terminate (with prejudice) power to any port that draws over 550 mA, until you physically power-cycle the hub. This is annoying for obvious reasons, especially on 7-port hubs with beefy power supplies, so most hub manufacturers don't do that anymore.
What the pi should do is monitor the voltage level of port it is drawing from, if it draws it down, it should turn on a fault LED or disable onboard services (like ethernet and usb).
