There have been cases that certain multiplaform games do well if they were exclusive to one console. For instance there was this talk that Enslave would  have done well if it was sold as an exclusive to one console or the recent Castlevania lord of the shadows, or any game as a matter of fact.

there are some games as a multiplatform doesn't usually means huge sales, as compared to selling it as an exclusive.

Honestly, games being exclusive only helps if the platform-owner is going to support the game if the game is exclusive to their platform. The rest of the time, it's just a fanboy dream that the game would've sold better exclusive (it may make more money being exclusive to a cheaper-to-develop-for platform though).

unless the multiplatform release is of significantly worse quality on one platform then I don't believe that is the case. All of this is speculation of course but especially due to the makeup of this gen multiplatform is best for most games since the ps3 version will maximize Europe and Japan while the 360 version will maximize America sales. Castlevania Lord of Shadows will probably reach 1million units and according to vgchartz be the best selling castlevania ever. Enslaved is just not worth it as a product considering it can be rented and beaten 3 times over in a week.

Really the only way exclusive makes sense nowadays is if the game is first party published or the publishers make a good deal with sony or microsoft to keep the games exclusive. The majority of consumers don't care if the title they buy is exclusive or not, but might buy a certain system if their most wanted games are exclusive to that platform hence why we are seeing very few exclusives not published by microsoft or sony.

Making a game exclusive will make it sell better on the one platform but in my opinion except if the port is very poorly done, will not let it outsell both sytems combined.

All Shooters, American Sports (NBA, NFL, NHL and MLB) and WRPG genre games on the 360.

All Sandbox, JRPGs, Racer and Hack and Slash genre games on the PS3.

Multiplat everything for the Wii.

I don't think that would work well actually maybe the Jrpgs on PS3.

But yet again wii owners would get everything so i'll be happy.

That's a statement, not a question. Next time put "Should" at the start and end it with a question mark. 

 No game will ever sell better as an exclusive then as a exclusive with equal marketing a developement budget.

 The only reason Nintendo, Sony or Microsoft exclusive games post sales comparable to multiplat titles is because Nintendo, Sony and Microsoft are very, very good at promoting their products and they can afford to do so, what with a good portion of their marketing budget being recouped from console sales and bigger game profit margins.

 Anyone who suggests exclusives sell more due to just being exclusive is simply short-sighted and can't see sales beyond what fanboys post on gaming forums like this one. 

Unless it gets a sweetheart promotional/publishing deal from the platform's first party, it should probably be multiplatform imo. And even then it's sometimes not worth it.

And Castlevania would've done far worse as an exclusive.

Doubtlessly it has benefited games like The Conduit, which got far more attention as an ambitious Wii game than it would have as pretty much anything else, and the early positive buzz on the "PS3-exclusive" Quantum Theory certainly could have generated more sales than the absolutely pathetic showing that game made in the end, but it generally only works as a marketing gimmick, and thus as games which would benefit more from a marketing gimmick than by standing on their own quality

@jarrod 100% agree

@Mr. Khan  are you kidding?? the Conduit sold terribly, I dont even think it did half mil.  Quantum Theory positive buzz??? That game failed because it sucked, I dont see why this is a hard concept, there is no cloak and dagger theories here. Crappy games for the most part dont sell well, and that is the way it should be