It's pretty big. It's not as big as Warner and HD-DVD, since FFXIII is still coming to the PS3. Sony just has no presence in America. Since Square Enix is adopting this whole "Worldwide" strategy, it's Sony's own damn fault.
I don't think we'll see any change in weekly sales though. It's big, but not huge. Let's remember that this game isn't as big as a GTA IV, and PS3 survived that. And there are still other exclusives, and reasons to own a PS3.
Don't get me wrong though, this shit is HUGE, and it sucks majorly for the PS3.







