Long question, with my analysis below: in order to maintain multiplatform support, what level of software sales does the PS3 need to sustain in order to justify continued ports from multiplatform developers?

I think we've heard several times (from heads of Ubisoft, among others) that porting from the 360 to the PS3 takes about 10 percent of a game's budget. That analysis has been challenged -- Ubisoft themselves have struggled with multiplatform development due to UE3 and other issues -- but is probably somewhere in the ballpark, and I think we can safely assume that even in the worst case, porting costs will go down as multi-plat engines are refined and should be (Again, at the worst) 10-15 percent of initial development costs.

Now, if we look at recent sales trends, we find that the PS3 is selling software -- especially multiplatform software -- at a more than reasonable rate to continue justifying development. In the last two months, the 360 has sold 9.2 million to the PS3's 3 million in total software in America (proof of these figures can be found in the thread here ), and in particular we saw that CoD4 and Assassin's Creed sold at almost exactly the 3:1 clip we'd expect, considering install bases, favoring the 360. Effectively, this means that third party companies can expect a 10-15 percent increase in development cost (at worst) to produce (on average) a 25 percent increase in revenue. 

Now, even assuming we're significantly off in any of these analyses, the actual software ratio should continue to tilt in the PS3's favor over time (even if the 360 does continue to outsell the PS3 in America, and I expect it will, it has not been outselling the system 3:1 and will the actual ratio will continue to average out to 2:1 or whatever the final sales ratio is) and there is no reason to believe that the PS3 will fall below 25 percent sales revenue any time soon. This analysis doesn't even include Europe, for which we are already seeing near sales parity between 360 and PS3, despite the PS3's smaller user base. In short, it's likely that most multiplatform games will continue to arrive on the PS3, and for PS3 owners, that's good news. If someone here disagrees with some of my analysis, let me know!

Interesting. Even more interesting questions are:

- what level of PS3 sales is required for exclusives to be financially workable? How many PS3 exclusive games have made a profit?
- in multi-plat games, what is required for most devs to give a damn about the PS3 versions, instead of launching defective software with framerate drops and other problems?

I just want multiplatform games that play as good as the xbox 360 version.

well in Europe PS3/360 games sell just as well if not better on the PS3, so ignoring any deals between microsoft and TP it is more then worth it.

I thought I read (from Reggie Fils-Aime, so it could be biased) that it was somewhere in the range of 500,000-1,000,000 sales required to break even on the bigger titles.

Good analysis Bod.Add to that the strong european sales and the way better position in Japan and we find a solid situation for the PS3 as long as software support goes.

 This would be for an exclusive title. I'm talking about games on 360/PS3, and whether simply making these games de facto 360 exclusives would be a good choice. My analysis says: no.

And as others have pointed out, Europe is a whole different bag of cards. Absolutely, that should be factored in, and furthers cements the PS3 as a legitimate multi-platform option.  

I think Heavenly Sword would be a title that paid for its budget. Its at 600k+ and growing.

But I agree with the 500k-1 mil range.

Yep, adding that to the OP now.

Edit: guys, this isn't about exclusives, as that would be an entirely different set of calculations. It's about multiplatform development. If you want me to really pierce the heart of the issue: will the PS3 suffer the software fate of the Gamecube, and simply stop receiving ports from third party developers? Answer: I think that's extremely unlikely. 

Indeed, the one thing missing in the OP is the budget required to do more than a half-assed port.  10-15% gets you bugs, framerate issues, etc.  How much did the developers spend who wrote two versions of the game from the ground up?