I am the developer. Regarding price, we decided to start charging because the serving costs were non trvial and I had been getting a lot of email requests for support that were taking up my time. Then Google App Engine prices went up too.

We didn't expect many paying subscribers and that is how it turned out, but we have enough to make it worth leaving the site up and running.

For low volume users we are thinking of offering a pay-go pricing option AWS style, with a low per-query price.

But this is not our main project now (WeatherSpark.com is) so I don't know when we'll get around to making changes.