This is the "FAIL EDITION", so no I'm not cherry picking, just staying on topic. I will do a WIN edition in a few weeks.

Machina# I mostly buy just ps3 exklusives as it would be to expensive to buy all games and with ps3 exklusives i no i will get quality. When i buy multiplattform games i only buy them if i really really want it or when they are cheap like when i bought Enslaved.

I actually agree that *some* titles will sell more if they didn't go multiplat. Demon's Souls comes to mind.

you are a fanboy , actually many devs have a very hard time programming for the PS3 cos is hard to put games on that hardware , bayonetta actually was delay 4 months just because the ps3 version have problems and many others games have the same issue , just look many interviews on devs about programming for PS3

Exclusivity helps in optimizing for a single console. Having to optimize for two consoles would make for longer development times since in this example the PS3 and the 360 are very different in architecture.
In terms of sales however, it may or may not be the case. If it is a new IP going exclusive might give it a boost as it creates a certain buzz for simply being exclusive and fanboys will grab the game for their loved console. Multiplats however work wonderfully with existing franchises that do not need the boost in marketing.
On a related note, new IPs can work if the developer has created a strong awareness of their company for example Rockstar. This is what most game dev companies lack nowadays. Creating a strong brand that people would recognize even in newer IPs.

However, a new company who has a strong ties with a particular console and has an established fanbase there may have a hard time going multiplat. As it may anger fans and the other console may not necessarily have a strong enough fan base to push sales.

Oops too late, i already commited to the "FAIL EDITION" but i cannot add to the fail. So i shall say nothing and wait for the "WINNING EDITION"

I am of the opinion that Ninja Theory likely would've been in a better position had they stuck with Sony and worked on a Heavenly Sword 2, but I disagree with your other example, and cases like Ninja Theory are certainly a rare exception.

Are you serious!?

Why are there so many over-sensitive, whiney people on this site!? 

Seriously not cool.

Moderated.

Tekken 6 isn't going to be the worst selling Tekken when all is said and done, either. Here's the list of the best selling Tekken games

Tekken 3 - 6.91 million 
Tekken 2 - 5.45 million

 Tekken: Tag - 3.94 million
Tekken 5 - 3.66 million
Tekken 4 - 3.31 million
Tekken - 3.18 million
Tekken 6 - 3.16 million

Now, in the past 12 weeks, the Tekken 6 editions have sold the following:

Ps3 version: 60k
X360 version: 16k
PsP version: 7k
Sum: 73k

Now, considering that it has sold 73k in from week 72 to week 84, selling another 500k isn't out of the question. Another 200k is a certainty. In other words, Tekken 6 is looking to end up selling pretty much exactly as much as the average of the Playstation 2 Tekkens.

It hasn't really failed at all.