It may be possible to put 4GB of RAM in the new MBP.
However, Apple technical specifications state a maximum of 3GB RAM.
It is for a reason.
The memory controller may be designed to address a maximum of 3GB thus the restriction. The actuall SO-DIMM would accept the second 2GB RAM module but the memory controller would not register and manage it.
That's my conjecture at least.
And as for the original poster's question as to why the huge price premium on the 3GB option, if you look at RAM module prices, you will notice that the price difference between a 1GB SO-DIMM and a 2GB SO-DIMM (SO-DIMM being notebook memory, which is usually more expensive than its desktop counterpart) is huge.
2GB DDR2-667 modules just recently started being available and carry the usual "bleeding edge" price premium.
People have to realise Apple doesn't manufacture computers.
The are a system assembler.
They outsource computer components (CPU, Videocard, Hard Drive, Optical Drive, RAM, LCD panel etc...) and put them together. They design the enclosures and have them manufactured to their standards by other companies that are specialized in this field (ex: AsusTEK and Quanta make enclosures for MB and MBP).
So if RAM prices are high, Apple charges more. In all cases, buying RAM from Apple is more expensive.
It would cost you less to get the 1GB shipping in ther MBP and add a 2GB module bought from elsewhere. But you would have to research the proper RAM, get it shipped to you and install it yourself and then making sure it works properly.
To some people, that is too much of a hassle and risk, so they are happy to pay Apple a premium for them to get certified, tested and warrantied RAM.
I hope that makes sense.
