What I don't understand is how other companies (eg. Sony Vaio Z series) manage to fit i7 processors within the same size body and people here claim apple can't -could someone explain please as I'm new to all this mac stuff!
Is the size of the case the same? If so is the battery life time the same?
For the Sony Z it gets about 4-5 hours less time. Chop 4 hours worth of battery from inside a MBP 13" and you'd have more space.
It is primarily a space and thermal problem. Likely need additional fan (which consumes space of which there is none). There was no place to put the additional discrete graphics chip and the required VRAM. If there was a huge empty spot inside that it would have been more practical to do.
Sony is also using a custom SSD "assembly" that saves on space (similar to Apple chucking the battery casing, Sony chucks the drive shell) It is not a standard part. That gets some incremental space back also.
http://www.engadget.com/2010/03/05/sony-vaio-z-with-quad-ssd-stripped-down-and-explained-by-its-pro/
follow the link there to the site with pictures. Looks like the DVD ROM drive may be custom too since not enclosed. They may have eeked some space out of using carbon fiber and not aluminum also. Sony is using a fan with heatpipe wrapped around assembly. Again a custom Sony thing most likely.
What is weird in those pictures is there is no sign of the battery. Curious where they stuffed it.
The sony also costs about $600-700 more. The other constraint is cost. If had to add more parts ( discrete GPU and VRAM) it will cost more. Apple wants price separation from 15" offering. Would not help to have 13" creep up on 15" pricing.