Cell phones and cable might be at least partially specific to zip code, though Sprint (which prompted this rant) has always claimed to have a Nationwide network that I would assume is pretty uniform. Perhaps their rate plans aren't exactly the same across the country? Why don't these companies just use geo-ip data? Its available, it might not be as accurate all the time, but I'm betting a bunch of people just flat out lie when prompted anyways (90210 anyone?).
But the biggest offenders are the various car research sites that all want your zip code so they can try and shove you into a specific dealer. Yes, I'm sure you get a lot of money for lead generation, but I don't want to give you my zip code.
These types of sites lead to a more generic class of problems with sites: when its easier to find information on a specific site by doing a site based search on Google then by navigating/searching on the specific site. If this is the case, you're failing the #1 point of the web: if you said marketing and making money, you've failed. Its finding information, the point of your site is information, you make your site easy to use, contain useful information, and make it easy to find that information, and boom, you have users ... which is the biggest step towards monetization.
Or maybe I'm mis-using these car sites, perhaps they exist more form comparison shopping of cars by "exact" value, and comparison shopping deals for one car from multiple places.. but I'm always using them for information way before I care about the price. They should be helping me investigate cars, and when I've made my decision on which car I want, then maybe I'll be interested in finding the best deal on that car. Forcing me up-front to think about actually buying isn't going to help.
Oh, and on a semi-related rant, why is it that Car websites make it so hard to investigate the interior of their cars? Its easier for me to go to a local Automall and take in all of the available cars in a class then to try and one-by-one figure out what the interior space is like visually online.