It's not a critics' list, it's a readers' list.
Seriously, how many people have even read (or should I say "attempted to read") The Silmarillion?
If you haven't read it, you aren't likely to put it in your top five picks.
And I don't know how how humor and hard sci-fi were on the list, but if you focus the humor votes onto one book, Hitchhikers would be it.
As for me, I have read it, and I have also read all of Le Guin's stuff hoping in vain that someday I'd get a glimpse of what people in college assured me was her brilliance. Nope. It's awful: only an NPR audience would put one of her books in the top 100, let alone several.