I agree -- that is indeed a clean and clever upgrade, and one I'd never seen before. As to your excellent question about why Apple did what they did (and didn't do what would've made more sense), perhaps it's all an artifact of Steve Jobs' opposition to expansion of any kind in the first place. The design team had tried to sneak in an expansion port disguised as a diagnostic port, only to have Jobs order it taken out. Perhaps there was a similar battle (again lost by the team) with respect to RAM upgrades? As you note, only a trivial address-decoding change is needed to work with the higher-capacity DRAM, so upgrading is truly simple. Very curious, indeed.