Yes, and no. Most of the arguments have already been said. Exclusive = more budget and more hype = more sales, but established franchises going multi-plat = more sales (COD, Devil may cry, Mass effect shortly)

A pretty good counter example to this would be Mass Effect (360 only, 1st party published) and Dragon Age Origins (PS3 & 360, 3rd party published).  Both were well received and sold amazingly, but both were also well handled by their publishers (unlike Enslaved).  Namco Bandai really is one of the most incompetent publishers around imo, I hope they don't torpedo Dark Souls success.

in some cases yes and in some cases no...but IMO going multi make some games bad...i mean i can remember these Final Fantasys,GTAs,Tekkens were all great games till they went multi from day one...

I think that people are generalizing a bit too much when it comes to this subject.

Can exclusivity help certain games perform better than if they were multiplatform? Absolutely. At the same juncture, though, going multiplatform can also greatly boost the performance of certain games.

Personally, I feel that it comes down to a case-by-case basis on whether exclusivity is the better option for a game. For example, I feel that the Gears of War series' exclusivity has greatly boosted its sales compared to how it would have performed if it was multiplatform. It's amassed a huge following, and it's one of the first titles that 360 enthusiasts list when they're trumpeting the 360's library. Had it been multiplatform, I have no doubt that it would have been successful, but I'm somewhat skeptical that it would have been as successful or if it would have amassed the same devoted following that it currently has. 

On the other side of the coin, though, I think that a game like Dead Rising 2 going multiplatform hurt its sales in the long run, compared to what it would have been if the series had stayed 360-exclusive. There was a certain love that many 360 owners had for the first game, and I've seen (admittedly anecdotally) that much of that love was lost when the sequel was released.

Do I think that a significant portion of that can be attributed to the series going multiplatform? Absolutely. Had the series stayed exclusive, I believe that the reviews would have been better, and that the fanbase would have been more likely to enjoy the title to a greater degree.

For one final example, I'll mention Enslaved. Had the title been a Playstation 3 exclusive, I believe that the title would have performed significantly better than it did as a multiplatform game.

Enthusiasts of any platform are far more apt to pick up an exclusive title, as it's something that their console of choice has that another console doesn't. Because of that, I think that titles (and new IP's especially) have a far higher chance of building up a fanbase and racking up sales than games that go multiplatform right off the bat do.

There's also the argument of the quality of games in the first place, the quality of the ports to the other system, the post-release DLC support for the other console's port, and how much games would have sold had they stayed exclusive in the first place, but in my mind I think that it comes down to a 25-75 split when it comes to games that would have benefitted from staying console-exclusive compared to games that benefit from going multiplatform.

It all comes down to a judgment call on the part of the game companies.

I think it depends on the game...a game like assassins creed would have suffered had it been a console exclusive for either ps3 or xbox. However a game like enslaved would have done better had it been an exclusive. I think what im trying to say is that games which have mass appeal would sell better as a multiplatform game, but games which are niche or not as popular would sell better if i was an exclusive. Being an exclusive game in this generation automatically gains the attention of the fan base of the particular console its on. I think infamous is a good example of this. Bearing in mind that infamous would not have received the attention it had got if it wasnt a ps3 exclusive, it woudnt have gotten the advertising either.

How is going mutliplat makes games any worse? Yes the game quality may have decreased but it was due to developer not the fact that it was catering for two more or likely the same audiences, you can't honestly blame a game being bad for going multi plat, the only thing that could be affected are graphics, slight tearing due to inferior porting.. To be honest, the games swayed from the whole "Have the fun" side to the realism side, as is proven by GTA4 and the gaming has morphed from something that was last gen, as more and more adult gamers become involved.

Well, it's not going to apply for every game... It really depends on where the core crowd is, or is willing to go..... Then, also, it depends on development... It's really different for every game...

Tekken 6, for example, should have stayed PS exclusive... They held back the PS3 version while they made the 360 version... Making the game take a year longer to be released... In this year, Tekken ended up having more competition, and the graphics of Tekken 6 were outdated on both consoles when it was released... And, for what?  An extra million sales?

It would have done much better being released a year earlier on the PS3, with much more appreciated details, and not as much competition around...

Then, there's other games... like... Call of Duty, which shouldn't be on a single platform.  If the audience is there (and worth it) it should be multiplatform... Otherwise, if the auidence isn't there, then, remind me who you're making the game for again?

And, then, the thing about games like Final Fantasy, you can simply store more on a single disc for PS3.  If you can't release the game on the system because of disc space, then, you have something to think about...

And then, finally, it's the exclusives as a whole.  The more exclusives there are to help the brand, the better.

Look at Lost Planet (sold almost 2 million on 360 and 1/2 million on PS3).  The first game sold well because it was one of the earliest, graphically impressive games for the system.  Of course, the game was shit but we didn't care.  It looked pretty and there wasn't much to choose from.  Now, look at Lost Planet 2 (sold half a million on 360 and half a million on PS3).  The game is "better", it went multi-plat, but the game is still shit.  There's more to choose from.  Now if I wanted to, I could twist things around and say that going multi-platform killed the games momentum.  That's not the case.  There's just so much more to choose from--games that are actually well received by the public. 

^^^Now, look at Saints Row.  The game sold 2million on the Xbox 360.  Saints Row 2 came out and improved on the original in every way.  Saints Row 2 sold 2 million on the Xbox 360.  It also sold another 1 million on the PS3.

Good question, It will be interesting seeing how Mass Effect evolves into a multiplat series, I know the first 2 as exclusives sold pretty well on the 360, now that part 2 is coming soon to PS3 and ME3 will probably be released simultaneously, Let's see how fans react. I know for a fact fans dont like losing an exclusivity, I remember years ago watching in TV Sonic fans refusing to buy the latest Sonic game for the Gamecube.