While I was playing a vs AI game, the cyclone and liberators were using a text to speech version of their voice lines instead of their normal ones.
I have noticed the same thing with the Adept as well. No other Protoss unit did it.
I find it funny that you guys noticed units doing it, because I spotted it with Donny Freaking Vermillion at the end of The Vermillion Problem. He was saying a line I had never heard before, too - maybe it has something to do with missing voice files?