Nope, re-read my post (or, if you want the insane technical details, read the PDF I linked to.) The xM965 chipset doesn't support the proper technologies needed to support 4 GB SO-DIMMs.
The xM965 chipsets support memory chip technology where each chip is 256 Megabits, 512 Megabits, or 1 Gigabit. 1 Gigabit is the same as 128 Megabytes. (8 bits equals one byte, 1 Gigabit equals 1024 Megabits, 1024 Megabits divided by 8 equals 128 Megabytes.) The xM965 chipsets support up to 16 memory chips per module (SO-DIMM.) 128 MB per chip * 16 chips = 2048 MB (2 GB) per SO-DIMM. The xM965 chipsets support a maximum of one SO-DIMM connector per channel, and have two channels. This makes a maximum of 4 GB.
The limiting factor, realistically is the 1 Gb chip technology size. In order to make 4 GB SO-DIMMs, you would need 2 Gb chips. xM965 doesn't support 2 Gb chips. Yes, if they allowed 32 chips per module, it could be possible; yes, if they allowed 2 SO-DIMM connectors per channel, it could be possible. But both of those are rather ridiculous in a notebook.
By comparison, the older 945xM chipsets used in the pre-Santa Rosa MacBooks/MacBook Pros also officially supports 4 GB (same technology limitations as xM965,) so the fact that Apple only supports 2 GB in the Core Duo models, and 3 GB in the Core 2 Duo models is a limitation of Apple's, not Intel's. The 4 GB limit for current (and likely future P35/G35-based laptops,) is an Intel chipset limit.
As I mention in my previous post, while the desktop P35/G35 chipsets only support 1 Gb chips, it is possible that the mobile equivalents could support 2 Gb chips, but since they don't even exist yet, I don't know...