It's entirely possible to make unconfirmed, baseless prediction guesses that can become truth at a later time.
Even if a PS3 port appeared a year or two later, it really wouldn't matter much except for those who were really late at getting into the ME franchise.
Case in point: by the time that MGS4 360 port shows up (if you were holding your breath for that one, you'd be dead by now), who the hell will even care other than the handful of people who clung desperately to the notion that it was a near reality.
If it happened in 2010, sure; that would be a pretty big deal, but it seems less likely now that the release of a port would be in the near future given that ME2 is doing quite stellar on the 360 and (maybe) PC. This is not to say that said port is not already in development.
But no one has really detailed the terms of "exclusivity" for the franchise. It could be a year or more for all anyone knows.