Wow, CS5 doesn't have "png.8bi" and I can't find it anywhere. And putting in "SuperPNG.8bi" doesn't change anything. I wonder if they hard-coded the Formats to save which come natively with PS.
Actually pngs can do both specific pixel value transparency (i.e. "the .gif way") and the RGBA style ("the .tga way"). In both cases I still think the user would be better served by Photoshop handling the image the same way it handles every other common format, or at least having an option to switch from the "special" PNG…