Zestful uses machine learning, so there could be a fair amount of storage, CPU, and memory requirements that make using a hosted API preferable to a local library. Also, if you read Michael's posts on https://whatgotdone.com you'll see that he is frequently improving the model. With a hosted API, customers benefit from improved accuracy immediately without having to update anything.
"Without having to update anything" seems a bit disingenuous - does this software even work offline, without having to ask for some data from an online server, just to load the front page?
