I know you couldn't under Leopard, but I was wondering if someone had tried doing this since the release of Snow Leopard. I know the latest MBPs all support 8GB of RAM, so I was hoping Apple now is letting some of the older MBPs do the same thing.
The only thing I can imagine is the lower limit imposed by Apple for the product (possibly because of cost, availability, firmware, etc.), versus the actual physical limitation of the hardware. Many times the two are different with Apple's initially being lower.