Under "Projects: Fundraising and Commerce": "Project Creators are required to fulfill all rewards of their successful fundraising campaigns or refund any Backer whose reward they do not or cannot fulfill."
I'm not convinced. The section you referenced pertains to the backing rewards only. They are, and always seem to have been, very hands-off about the delivery of the project.
e.g., "$50 tier, get a copy of the game"
Unless none of the reward tiers involve the project itself, and are all things like t-shirts and stickers...
The project purpose is to make a game. That's separate from the reward tier "get a copy of the game". So if the project fails, the backers who bought a copy of said game need to get a refund.
Do projects really setup their own contracts with their funders?
Whether it holds up in court is a different question, but this lawsuit at least gave a precedent.