Really, really doubt this is happening.
And if hell freezes over and it happens, it won't matter, everyone who wants it will have played it. It just means it will have less traction with PS3 owners, in my mind I will always see Mass Effect as a PC360 franchise.
I don't understand the surprise about the GTA4 DLC, it's always been known it would eventually come out on PS3/PC, just like the Fallout 3 DLC. Nobody ever made it much of a secret. But, like expected, it would come much, much later for non-360 platforms.