AdobeStandardEncoding is a specific mapping of certain glyphs to certain cells; in this respect it resembles FontSpecific encoding. Because it is standardized, the array is not spelled out in the PFB file; the line
/Encoding StandardEncoding def
tells Adobe Type Manager (ATM, either the Windows and Win-OS/2 version or the native OS/2 version) that the encoding is "standard," and the environments are expected to know what this standard is without having the array spelled out in each font file.
Although AdobeStandardEncoding is a real mapping, there is an importance difference between it and various FontSpecific mappings: operating environments are expected to remap AdobeStandardEncoding fonts according to their own requirements. That is, although AdobeStandardEncoding does assign glyphs to cells, no operating environment actually uses these assignments and any environment remaps the glyphs before rendering them. Confusion arises because Windows and OS/2 remap such fonts in different ways.