Some Googling revealed that a faulty USB device may fry the entire motherboard+processor of a computer if it is not fitted with appropriate fuses (if it is known though, I wonder why they wouldn't!), however I wonder if other devices on the same hub could be fried as well?
Edit after Olin's answer:
I don't mind killing the hub, but I do mind that the PC or the USB devices are at risk. Does that mean that it is risky to have USB devices which are powered from mains because they could theoretically fail and apply mains to the hub, take it out, and in turn apply mains to the other devices' USB receivers? But isn't that theoretically possible as well that a 2.1 sound system fail and apply mains to a 3.5mm jack as well?
Best Answer
It is possible, particularly if the device is self-powered. Attempting to draw too much current or even a dead short will not hurt a proper USB host port. However, accidentally applying high voltage to either of the data lines could be bad. At least that could blow out the drivers for that port, but it's no stretch to imagine it could take out the whole hub chip.
This is not a place where fuses are reasonable and would do anything useful anyway. By the time a normal thermal fuse trips, the hub chip will be long dead. Putting anything else in series with these lines is a problem since they have to carry high speed signals. The hub chip will have protection diodes or similar to power and ground. That will protect against the occasional static discharge. Protecting against anything more than that would be expensive and not worth the extra money for the very rare case it saves something. It makes no sense to waste even a few pennies protecting a $50 motherboard when this protection will only matter once in every 10,000 cases.
You can't apply line power to the audio jack, the video output, and most other external connection points of a PC. I don't see why USB should be singled out for extra and burdensome protection.