Exclusives often get a different kind of backing. They get more advertising, more resources for developement and more media coverage. They get mentioned in press releases. They often have high-profile studios behind them.

The same game with the same hype would sell more as cross-platform. But of course, life isn't that easy.

Then there's also the issue of multiple console ownership. In America at least, multiple console ownership is up tremendously over last generation. This would help to negate the edge of the extra install base.

well it's easy to think that when you can think of it as if today they were released on other platforms but at launch?  If some of the games loose their marketing and backing from sony or microsoft they could very well have sold less on the one platform they were on and if there isn't other marketing to replace it.  Sales aren't only a relationship between how many people can buy it.  There is also a realtoinshipa with how much it's marketing who it's marketed to and what it's competing with.  Sometimes though the "fanboys" buy something that is just on their console if one game is multi and a similar game exclusive they would pick up the exclusive.  There is also that sometimes when a game is multiplatform it doesn't work great on any of the the platforms its on but when it it made for just one it can work really great on it and that can lead to more salse then then would be had for doing the multiplatform version.

I do believe though that most cases being multiplatform will cause a game to sell more that would more that regain any costs of making it multiplatform. 

No. Not at all.

Seriously, on two consoles it would sell more. Simple logic.

I say not really.

Like say Halo 3 was multiplat it would have sold just as much on 360 as it has, and probably a few million on PS3.

I guess exclusives do sell well if they're advertised well and they're of high quality because if a game is exclusive to your console you get excited and want to try it...but no amount of arguing could convince me a game like Halo 3 would have sold LESS then it did now if it was multiplat.

Exclusives get more marketing and bundles so I think it probably can in some cases, but mostly no.

Well depends on the game.

Lesser games depend heavily on the stupidity of the average consumer, so them more platforms its on the more likely some one will just pick it up.

Games like DQ FF GTA would sale the same if not better being exclusive. Going multi wont really hurt sales early on but i think it hurts the quality and prestige of the franchise and eventually the sales will suffer.

I don't think it will.

If for some odd reason Halo went multiplatform (it never will, just using it as an example) it would piss a lot of people off, but it's still Halo and the Halo fans are still going to buy it.

The people who have the other system but no Xbox now also have access to the game so that opens it up to more people. There will be those stubborn other system users that will never buy it but FPS fans will, so still more sells.

I don't agree

and if Halo went multiplatform it would sell as much as COD does & possibly even more

Obviously it depends on the game. Certain genres tend to better on the 360 while others do better on the PS3.

Although, when in comes to shooters inparticular the 360 has a massive advantage. Which most likely comes from Halo.

It really depends on the game.

New IPs will often sell better as exclusives than they would (imaginably, we can't be certain) have as multiplatform. This is all to do with the marketing/bundling of the game though. Resistance: FOM or Motorstorm wouldn't have sold anywhere near as many copies had they been multiplatform, as they wouldn't have been bundled so heavily. Similarily, it's hard to see games like LBP get as much marketing as it did, if it had been multiplatform.

Established IPs, such as Halo (example, not saying its going multiplatform of course) would almost certainly sell better as multiplatform. In the case of Halo, the brand has been built. Current fans on the 360 would continue to buy upcoming releases (unless quality dipped massively of course, but that isn't to do with exclusive vs. multiplatform), except for possibly a very small number of near-religious fanboys. The sales to make up for those boycotters, as well as add more sales, would then come from the other systems the game becomes available on. They sales wouldn't double (assuming console base A = console base B) due to genre preference between consoles, as well as multi-platform system owners, but I feel certain that the sales would increase a considerable degree regardless.

To sum up, it really comes down to the IP.