To get really picky though, I thought the official line was that
Wikipedia is a *project* to *build* an encyclopedia. Or maybe
"Wikipedia" is the name of the encyclopaedia being built by "The
Wikipedia Project". In that case, half of the entries at WP:NOT refer
to the project (wikipedia is not therapy, a game, myspace, a chat
site) and half refer to the actual encyclopaedia (not an
indiscriminate collection of information, not a jargon file etc).
To answer your original point though, "why expand WP:NOT"? Basically
because the nature of Wiki means that people can endlessly expand the
project in new directions. Saying "WP is X and nothing but X" doesn't
really pose any limits on this expansion. Saying "WP is X, but
definitely not Y or Z" does.
Steve
There's at least 2 sections in WP:NOT. One which explains what the project
is not, one which explains what the articles are not. BTW, I do agree with
that last paragraph. You can say Wikipedia is a free encyclopedia anyone can
edit, but some people don't seem to grasp the idea of what an encyclopedia
is, so while it's unfortunate we have to use negative language "Wikipedia is
not a vehicle for promotion" is something we need to have in there. Even if
it's just so we can point people there. It's easier than explaining what
type of content is encyclopedic and what isn't.
Mgm