MacBook4,1 has 64-bit EFI:
Code:
MacBook:~ k$ ioreg -l -p IODeviceTree | grep firmware
| | "firmware-revision" = <0a000100>
| | "firmware-abi" = <"EFI64">
| | "firmware-vendor" = <4100700070006c0065000000>
MacBook:~ k$ ioreg -l -p IODeviceTree | grep product
| "product-name" = <"MacBook4,1">
MacBook:~ k$
Running SL, I would guess that the only thing holding back my machine from being able to run a 64-bit kernel is the lack of 64-bit drivers for the Intel X3100, despite those drivers being available for Windows.
No doubt Apple could make these machines run the 64-bit kernel. I think some sort of petition or false advertising complaint would be a good idea, or these devices will be put in to forced retirement in a few years when Apple drops the 32-bit kernel (just like PPC machines have been dropped earlier than a comparable product would have been). My BlackBook is just over a year old, and I'm nowhere near thinking about replacing it.