I've seen those postcode and address validators @CollectibleMad and they are quite handy. I have not seen that kind of app for Website Builder? I assume that you are validating the addresses manually? I don't know who you ship with but the USPS shipping tool will validate before you can ship the package. Hopefully whatever method you are using you notice these errors before you ship a package.
The great thing about GoDaddy and their Website Builder product is that they are always adding functionality. Blog was a highly requested feature and it was recently added. Since there are tons of features and apps on Website Builder and being added I don't see why address validator couldn't be added? Not that it helps in this situation but Website Builder Help is a great resource as well.
Please also note that the more a feature is requested the higher priority it will become. GoDaddy welcomes input like this as they strive to make their products better. I'm sorry that I couldn't help more.
...turns out that my two cents is worth less or more depending on the current exchange rate.
roy darling *my posts seem a lot shorter in my head