> Accepting all common forms for
> encoding names means that you can usually give Python an encoding name
> from, e.g. a HTML page, or any other file or system that specifies an
> encoding.

I don't buy this argument.  Running attached script on http://www.iana.org/assignments/character-sets shows that there are hundreds of registered charsets that are not accepted by python:

$ ./python.exe iana.py| wc -l
     413

Any serious HTML or XML processing software should be based on the IANA character-sets file rather than on the ad-hoc list of aliases that made it into encodings/aliases.py.