Why not make missing alt attribute a warning?

Hello there,

  I've been creating a virtual enterprise website from scratch for the past
few months.  I have seen my website under w3m and other text-only browsers,
and I'm wondering why img has to have the alt attribute or else an error is
returned.  The W3C validator clearly says that "An img element must have an
alt attribute, *except under certain conditions*. For details, consult
guidance on providing text alternatives for images." and those conditions
are met by many images that I have.  The virtual enterprise website ranking
ranks negatively on html errors, but ignores html warnings.  I was
wondering why the validator does not list them as warnings instead of as
errors.

Brandon Lu,
VP of Web Design at Continental Grubbin'