There were scenes in UC3 where they used "cutscene quality" rendering during the game itself. I remember there were few, but one near the very end of the game where you're holding by one hand is what I can come up with on top of my head.
You're right about facial animation though, that's never been as good in realtime cutscenes.
I'm convinced they render all this stuff using their engine on PS3, image quality is still the same, the question is just at what framerate and how much memory each cutscene uses up. The most I've seen of them demonstrating this stuff running in real time is a report on IGN that said they had an interactive flythrough that first trailer of UC2.
Sure they use their engine...but they use 8 PS3s to render the cut-scenes.
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