The USPS provides a free service for address validation. You have to register an account and receive an access token. If they feel your token is using too much, they can handle it as necessary. Why this same concept couldn't be done in the same way is just lack of imagination.
You can access for free, but if you abuse or break the TOS your access is revoked. Done
So someone can host a ripoff NPS app on the App Store and taxpayers now pay for content hosting?