It's funny ,,,last month they said firmly that it's 360 exclusive ,atleast timed exclusive,,,,but today :
" Will Mass Effect 2 be an Xbox 360 exclusive again?
We haven't announced any specific plans yet with Mass Effect 2, so other than saying that I love the Mass Effect universe, I'll have to plead the fifth on this one!
"
http://www.joystiq.com/2008/05/23/joystiq-interview-biowares-ray-muzyka-talks-mass-effect-2-dlc/
It's a possibility that EA is forcing them to do a PS3 version since the highest game-selling platform for EA ,in the last quareter, was PS3.