VGX vs. PI Shading: Dithering

[devans at SNOWHITE.CIS.UOGUELPH.CA]

  A while ago I posted a question about shading differences between
a VGX and a PI (basically the PI looked much more blended, while the
VGX was "mathematically" correct, but rather harsh.)
  It just hit me that the cause was the fact that PIs have only 24
bitplanes.  So, when I used double buffering, I really got 12 planes
per buffer.  Then the pipeline dithered to make the colours look OK.
I have no idea how many planes the VGX has (I'd be interrested in
knowning, though...), but I'm sure it would have 48....so it could
do full 24-bit double-buffering.  That would explain the "soft" vs.
"hard" look
  This seems too simple...am I right in my assumption?