Ask HN: How does Gemcutter support itself?

http://gemcutter.org/

Gemcutter seems to have displaced Github as the gem host of choice these days. That's not a plug - I have no dog in this fight.

But I am wondering how reliable they will be over the long term since I don't see much evidence of a business plan. They prominently display the Heroku and ThoughtBot logos on the main page.

But there must be more to their business model than simple sponsorship?

Or it simply not very expensive to host all of the world's gems?