You're changing your argument now, your original claim was;
But now you're claiming it's because they're multiplatform? Right. Just please be consistent.
Ok then how about this, multiplatform games in general are VERY rarely optimized for the more advanced system whether they are made for a console first or not. This is fact.
Both the games I listed were developed on the PS3 and ported to the Xbox after the game was completed (but before gold master), Final Fantasy XIII is also in the same boat. It'll be interesting to see how that fares.
Find me where GTAIV was stated that it was first developed for the PS3, either way my previous statement still stands and like I said Ghostbusters had graphical issues on the PS3 that were patched.
It most definitely can not. It was patched but it still isn't close to the detail of the Xbox version. The developers even detailed the reasons why it looks so bad compared.
It most definitely can because it's still a multiplatform game.
It took 3 years to get a game like Uncharted 2 out, a game developed by a studio that only works on Playstation titles and claimed that "slowdown makes a game seem more impressive". It looks vaguely realistic, but so does Forza 3 on the Xbox.
That's funny. So just because it takes a while to get a game out means it should be discredited? 
Also Forza 3 has jack **** on Uncharted 2. The lighting effects in Forza 3 are mediocre at best when compared and the damage effects aren't too great either.
How many DVDs does Crysis, GTAIV, Oblivion, Fallout 3 or any other epic scaled game take up? MGS4 used lots of uncompressed video cutscenes and sounds. Compress those with H264 and you could fit it on DVD. As a developer myself (and the subject of lectures I've attended), MGS4 is just an uncompressed game that was used to promote the benefits of Bluray as a gaming format.
That's ABSOLUTELY HILARIOUS because Hideo Kojima himself stated that even Blu-Ray was not enough space.
http://kotaku.com/362807/kojima-says-blu+ray-disc-doesnt-have-enough-space
Maybe YOU should just stop spewing random crap around.
It might not have been originally developed for that but have a look now. 4 years later (is it?) and it supports 1080p60 just like the Playstation 3.
Looking at it now it still doesn't do true 1080p, again did you even watch the video I linked you to?
And every 360 game can be put on the PS3, it just suffers in the graphics department.
This actually made me laugh. See LagunaSol's post.