Half life does though, don't you remember when I plugged in the optical mouse into your ps2 and I was shooting all the good people. I remember that you took a little while to figure out what was happening.
Do you have any sources that varify this? I mean, it makes sense, but I've not seen anywhere that talks about it. I've seen some that do support the USB headsets though.
They support the keyboard - it's an alternative to using the onscreen keyboard which, takes ages to click each key. It also explains why people can chat sooo fast online.