Why do we enter city and state in web forms?

Why do we need to enter city and state in web forms? Once we enter our zip code, why don't city and state get populated?

With just a little more thought in the design of web forms, how much effort could have been saved?

If 100 million people in the US are regular active web users, and they fill in their name and address once every two weeks, and this takes 5 seconds, the total time cost per year is

100,000,000 * 25 episodes per year * 5 seconds per episode * 1 hour / 3600 seconds =

3.5 million person-hours per year

If we value that time at just $10 per hour, that is $35 million per year. Will a programmer please redesign the web form, to ask for the zip first and then perform a lookup for the city and state fields?

Thanks!