If you choose to assume instead that its because of the "PS3's superior capabilities" then thats fine but I see nothing in the interview to support such an assumption.
What about the last line then? (check the bolding )
And the point is that we're more prepared today for PlayStation 3 than we were for Xbox 360 this time last year, and the engine is running a little better
Wasn't that UT3 demo already running @50fps 2 years ago at GDC on PS3 (devkit)? I remember some quotes from back then...