Anyway 256 icons aren't much different from png 24bit icons. For our eyes there isn't difference.
The main difference between 256 colour and PNG icons is Alpha Channel, not the number of colors. The difference between a 256 colour one and a PNG can be minimal, but it can be like two planets apart. Depends on the icons. Alpha Channel is mostly used to provide antialias to the edges, or for providing shadows or transparency. It's rare when the number of colours comes to play, but given that PNG icons are usually larger, 256 colour ones soon loose the battle.
However, I liked Mason's older icons better. Many give the impression that there is something lacking with their edges.
EDIT
Never forget, 256 unique colors are only 16x16 pixels. :-)