For a while now NW has been selling but not publicizing Z fares (non-refundable ultradiscounted WBC fares, requiring 60 day advance purchase, e.g., $2100 west coast to Europe). Why don't they just let you buy these on-line, and why don't they publicize them?

I only heard about them (pre-FT) when I was trying to get an upgradable fare to Europe for last fall and upgradables weren't available, but Z fares were.