Double disk failure is improbable but not impossible.
The most impressive thing is that there seems to be no dataloss, almost whatsoever. Whatever the backup system is, it seems rock solid.
EDIT: My response was based on some edits that are now removed.
It seems the perfect circumstances to really last. It doesn't have an invasive business model, or investors screaming for ROI either. That's the kind of thing that often leads to user-hostile changes that so often start the decline into oblivion.
Also, I would imagine it's pretty cheap to host, after all it's all very simple text, I don't think it hosts any pictures beside the little Ycombinator logo in the corner :)