I'm not even sure what you are trying to say with this first sentence. As to the OS IPhone is more or less UNIX with a lot of the utility functions missing. Obviously Apple has gone in a different direction when they borrowed the core of Mac OS/X here but the fact remains you have a multitasking OS without a pageing system. That is no virtual memory, so real RAM is very important. More importantly iPhone OS is still growing in size and version 4.0 is due in very short order.
I'm not sure why you bring up the new processor as that has very little if anything to do with this issue. Apple could have used the current iPhones processor and the response would be the same. With out RAM a processor is pretty useless.
Validated? What year is this? Seriously the relationship between RAM and computer capability has been known for years. You question is seriously sounding like trolling.
In any event the easy question to ask here is this: have you used an iPhone? Apps are being hit with performance problems or failures all the time due to the lack of RAM. On iPad your RAM demands only go up due to the larger higher pixel count screen.
That is a good question! In a nut shell because it is feasable technology wise and would more than double RAM available to applications. Don't forget that a good portion of that initial 256MB will never be available to user apps. Some will go to the video function, some to the kernel and some to mandatory background processes. Right now developers are reporting less than 200MB of RAM actually available to programs. This is a step backwards not forwards.
Beyound that an additional 256MB makes apps possible that aren't currently without putting to much of a demand on the hardware. It should be enough to address regressive behaviour seen in many current iPhone apps. Finally more RAM makes life easier for developers thus leading to fewer bugs. Not too that the RAM issue only gets worst if multitasking becomes real. For that matter finding RAM to generate images for printing, if that becomes real, could be an issue for some programs. The list could become very long if you put thought into it.