1) I don't think Table 2 "defines" US-ASCII. A character set Content-type
should define the sequence of glyphs the users sees and the rectangular
arrangement thereof.
US-ASCII is not a Content-Type. In RFC-XXXX's terminology, it is a
character set, which is a subtype of the TEXT Content-Type.
Also, the table shouldn't list only the glyphs. It should list the
code values as well. The whole point of the "character set" subtype is
to indicate what kind of character encoding is used in the body.
Erik