If you are planning on using USB, there are a couple of options open to you, you can use a converter chip made by FTDI on board the hub. This takes a serial input stream, just like your PC, and handles all the nasty complicated USB stuff for you. The PC will see it as a virtual com port, and you deal with the information as you would with any serial port data.
You could have just a serial port on board the hub, and use a converter lead, it's one of those things with a bump in the middle, again it will be presented as a virtual com port to the PC, but depending on which one you use, it may require a proprietory driver to be loaded. Not that this should present you a problem, but it's an added unknown.
You could use a microcontroller that has a USB port on board, this could also serve to gather the data from the participants' input. The drawback is that you would need to learn to program the microcontroller of your choice, or have someone in one of the computing courses at the college collaborate with you, perhaps a divide and conquer approach might be more beneficial.
Lastly, you could forget about USB altogether and just stick with a serial port on board the hub, this still leaves you with the computer side of things to deal with, but should be easier and a little cheaper to build.
I would suggest that you forget about the simultaneous voting in as far as actually trying to detect, log 10 simultaneous events, and pass it on. It will be better for you to detect and latch each voter's input, then after all voting is complete, gather the information and pass it along to the PC. If you watch those things on the TV you will see that they count up as the folks vote, it's not an instantaneous thing. In the case of USB or indeed any kind of communication with a PC, I don't see any way round having some form of overall intelligence in the hub to gather up the information and control proceedings. This will unfortunately involve you in programming a microcontroller or some other semi intelligent device.
One possible idea comes to mind, build ten parallel to serial converters for the participants' button boxes and tack on an FTDI chip interface to each. Plug 5 each into two cheap USB hubs. That way it's mainly a software issue for the PC to read the 10 virtual com ports and graph the results. Just a random thought...