Yes, but it is no guarantee of course. Even with a large userbase, which is something a lot of developers had to learn on the Wii over the last 2 years. First and foremost the benefits of exclusives are:
1. Cheaper than if the game was on multiple platforms (in the same form)
2. More "spotlight", giving it an advantage over titles that aren't exclusive
Obviously, still comes with the risk, of not as large of potential customers. Exclusives, i would say are more risky than multi-platform titles, but the benefits of a successful one I think are far greater than a multi-platform title.
The problem what you are seeing with there, is there have been very few exclusives this generation that are of the same quality, AAA budget, and marketing of the multi-platform titles. Really, the only extremely successful ones have been coming out of Nintendo, which isn't something surprising. Outside of Nintendo, the main successful ones have been on the 360, with also some first party involvement with Halo and Gears of War.
Really, the problem is trying to differentiate these exclusives from the mass of popular multi-plat titles that are just taking over. That "exclusive" advantage for spotlight, seems to be fading because the multi-plat games are bigger. And I really think this is a failure on the makers of the game, as they aren't taking advantage of that "exclusive" marketing they have. None of them are willing to take that extra risk to make it as big as it could be, because failure is just so daunting this generation.
I still think that exclusivity can help a game's sales, but you have to go all out when you do it. Obviously, you won't get Nintendo like success because you'd need some extreme brand recognition to accomplish what they do, and maintain it like they do. But if you put the same effort they do (what Ubisoft has quoted as Nintendo quality) then you can at least you say you tried. I see very few companies trying that with their exclusives. They'll attempt that with their multi-platform titles but not the exclusives ones. And I think that'll be a trend for the rest of the generation, especially as the motion sensing market starts to mesh as well.
