Fail logic, there prof. First you are picking some examples that do not represent the whole scenario. As others have pointed out, there has been games that going multi-platform have helped them, and others that stayed exclusive and has lost sales.

Additionally, some of your examples are mixing main line games with spin-offs, that shows how weak is your claim.
Finally, FF XIII is garbage, it's good that sold less, however, as someone has already noted FF main line games have been selling less, and no one has sold more than VII.

And, seriously, what did you expected devs to do, PS3 was doing some bad bad numbers, if it wasn't by going multi-platform, some games wouldn't have been released.

Nah, you're pretty pesimistic. I can predict that PS3 does not pass the +5 million units (lifetime) and that 360 can crack up to 1.5 millions (and) more.

For Persona and KH its because we haven't had a mainline game forever

Both haven't seen one since the PS2. : /

And it looks like you know 0% percent about Sony exclusives since pretty much none of the games you mentioned where ever true Sony exclusives.

PWNED!

Most of your examples were inferior games compared to the current market. Is it such a shock that inferior games sell less?

Exclusives are games only on one platform. Not first party. Wow that comment and idea...just utterly hilarious O.o

You're even ignoring that many exclusive sequels have lower sales.

LBP > LBP 2
Resistance > Resistance 2 > Resistance 3
Crackdown > Crackdown 2
Forza 3 > Forza 4
Halo 3 > Halo Reach
Warhawk > Starhawk
Super Mario Galaxy > Super Mario Galaxy 2

and much much more. If a multiplat sequel to those games would be on par with the latest game in the series I'd say it was definitely worth it as the trend was going down.


EDIT: Doesn't have to be first party games either. But there aren't many examples of third party exclusives that stayed on only one platform.

Wow, nice spin.

Tekken 3 sold over 7 million units on the PS1. The series was on a sales decline as other fighters were.

Crash died because people lost interest in that genre. Even exclusive platformers from PS2 to PS3 struggle.

Kingdom Hearts declined after the first released. Even before it went multiplat.

Persona 4... you're comparing a spin off fighter? That's reaching. Although, I'm surprised they brought it the 360.

Katamari was clearly on a decline. The second PS2 release also did less.

FFXIII seems to be polarizing and its combined sales still out performed many other FF games.

Once again, you're comparing spin off. Nobody expected MG RISING to be a big hit. Also, MGS4 was supposed to the finale of that saga. MG Rising is just more story. Same reason why GoW3 sold significantly better than GoW:A.

GTA4 may eventually pass the PS2 numbers of San Andreas. In fact, it probably already did with digital sales. I've seen it on sale many times on PSN and Live.

I genuinely feel fans were fatigued with the release of DMC4. The latest game being a bomb is another story.

I don't believe the Tomb Raider games are tracked properly. Most notably, Tomb Raider Legend. Also, Tomb Raider was always multiplat. The first game was on the Saturn and I believe every release was on the PC.

Multiplatform development definitely doesn't always work out.
The lack of sales could be because of something else though.......the high entry-price of PS360 at launch(and even today) + the troubles transitioning into HD development.