I seem to remember when I first signed up, I didn't include the zone or area info only because I completely missed it when signing up. If it works like most sites, you sign up with email and password, get an email back that verifies the email and you click the link to log in. And the majority will probably just start using the site (as I did) and not bother going into their profile. So a lot of members that don't show that info could have just simply missed any place to enter it and it may not be a privacy issue. It is just general areas listed, it's not like you're giving your address.
Maybe a popup notice for newly signed up members suggesting they remember to list their area and zone so they get the help they need, or a reminder in the email (although I'd probably miss it in an email, I tend to just look for the link to click).
