> I think you mean the maximum memory which this model can use,
> not only the maximum MorphOS can use. Mac OS X can use the full
> 2 GB of RAM in the PowerMac3,3.

I guess that's why his list says "Anecdotally, PowerMac3,1 - PowerMac3,3 may also support 2GB ram" some lines below ;-)
1.5 GiB is actually what Apple claims as maximum RAM for both the PowerMac3,1 and PowerMac3,3:

http://support.apple.com/kb/SP123
http://support.apple.com/kb/SP117

The fact that they also work with 2 GiB RAM is more or less unofficial. I don't know where boot_wb's "Max 1GB" for the PowerMac3,1 comes from, though.