Obsidian's stated they want to make it equal on all platforms. So hopefully, it'll come out on all systems at the same time.
On the other hand though, the PS3's Cell processor utilizes a different architecture than the 360's Xenon processor, which has an older architecture. Most companies (not including Infinity Ward with this one) release their DLCs on the 360 and PC before the PS3 if it's on all three systems since the architecture of the 360 and Games for Windows is so similar.
I do hope that those of us in the PS3 community get it around the same time as the 360 and PC community though.