Just a followup up...
... When you change your zipcode through Settings/Edit Profile route, you will *only* be presented with a list of available city choices *if* there is more than one city name available for your zipcode. If your zipcode has only a single city assigned to it then you will not be prompted to select a city and the zipcode will be all you see. However, when you submit your zipcode change to the server, the City, County and State information will have been automatically set correctly for your zipcode.
I really wish there were a way to disable editing through the "My Profile" page, the programming that it takes to manipulate the City, County and State changes is pretty complex and unfortunately does not carry over well to the "My Profile" page ... that and it is kind of silly to have two seperate panels for editing the same profile (at least IMHO!) -- it just makes profile edits more confusing!