Britt made some valid distinctions between illustration and fine art.
However, as a practicing, professional "fine artist"  who works hard and well
at it I probably have a slightly different viewpoint from Britt's about the
differences. I think of the issue this way: Illustration is to fine art (or
expressive art) as journalism is to fiction.  All are valid endeavors, with
illustration and fine art using many of the same skills and tools, just as
journalism and fiction use the same skills and tools but to different ends.
Fine art belongs with those other "useless" professions such as dance, music,
and drama.  Illustration belongs with other "practical" arts.    As for the
$7,000 a year which someone found to be the average income of artists, I
believe that refers to fine artists. Designers, illustrators, art directors,
et.al. in the commercial businesses make, on average, considerably more.
Joan (she who, to feed both mind and body, works in both camps)