Anyone notice that the weapon reload sound in the Bootcamp Unity 3 demo level is straight out of Counterstrike?
Yahtzee!
To reach deadlines many game studios will outsource certain parts of game making and/or buy assets from third parties. These assets can include audio files. So even if it’s the same sound there’s the possibility that Valve and Unity bought and used the same asset from a third party.
As far as I know any part of any Unity tutorial can be used even in commerical Unity projects so I’m sure Unity hasn’t ripped audio files straight out of other games.
For the record multiple sounds from well known games like Starcraft and Red Alert can be heard in a multitude of music videos and other productions. They could all be ripped from the games, but I doubt it. 
the demo wasn’t build by UT themselves. It was build by a brazillian game dev (Aquiris), so it might be possible that Aquiris has made a boo boo, and UT not being aware of it? It could also be a sound in the public domain, being used by both parties (valve/UT through Aquiris).
Oh I highly doubt UT actually said, “Hey, let’s jack this sound.” I sort of doubt Valve would use a public domain sound, but I could be wrong. Also, using sound clips in things like music can fall under the fair use laws, so it doesn’t surprise me.
While I suspect it isn’t exactly legal, I found it amusing more than anything.