Just as a note, I know that for e-commerce shopping cart forms, we specifically force users to enter their address information and zip code.

No matter what you think, users aren't paying attention to what they enter in the forms. Forcing them to enter their address and zipcode allows you to do a cross check to make sure they entered everything correctly.

You may find it annoying, but when it prevents people from ordering items to the wrong address, it's a pretty useful extra field.