I simple explanation for the Zorro2 graphics boards configuring as an I/O device and VRAM is the Zorro2 memory map which separates Zorro2 I/O and memory functions. (This is not the case for Zorro3 boards but my GVP Spectrum still configs one device in Zorro2 I/O space even in Zorro3 mode).
As far as the other similarities it may have been done for software compatibility or just because the boards use the same graphics chip. The PicassoII being one of the first real RTG boards was in a good position to set some standards.
Last edited by SpeedGeek; 19 July 2013 at 15:09.