[ajross]

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.

[throwketchup]

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.