SpringHeeledJack,
Well, to be honest I've never really put much thought into RAM limits until this question came up !
I've always just understood RAM limits to be a predominantly hardware limited thing.... combined with the occasional software limit (e.g. 32 vs 64-bit, and Microsoft/VMWare licensing limits).
Which is why I would be surprised if you can do anything to something that's as deeply engrained onto a motherboard and CPU (northbridge memory controller hub) .... but if someone lurks here who's spent time system engineering for a modern manufacturer (not really interested in tales from the computing dark ages) , I'd be happy to be shown evidence to the contrary !
I guess you may be onto something that larger RAM modules may not have existed as commonly "back then" when Apple were designing those models as they do now ? But I still think its more of a CPU/motherboard hard limit than what Apple were able to test with ?
In the mean time I'm going to spend a couple of minutes on Googoo to see if any definitive looking answers pop up ....