Not especially, in my opinion. In light of his comments to the effect that Reader was a failure because it didn't achieve 100M users, I'm not even remotely interested in whatever Storyworth is.
Big companies often have arbitrary guidelines such as "only billion dollar lines of businesses are worth having". In this case 100M users may have been the threshold where $1B/year in revenue from the product was realistic.
It seems like a large number, but at Google's scale it might actually be rather small. Google is a large company, and each product is something that takes resources that could be better spent somewhere else. I don't expect Honda or Ford to keep around a car that only sells a few thousand a year, knowing that it requires continual work and refinement, space in their plants to build, space on the lots to sell, and a business strategy. I don't expect Google to act any differently.
The real question--unaddressed in these tweets--is why Google insisted on such a large user base to keep a project going.