Interestingly, the KickStarter FAQ on this topic says:
However, the "this" that they refer to is:
https://ksr-assets.s3.amazonaws.com/creator-responsibility.png
I'm no lawyer, but that looks very vague, hand wavy and barely enforceable to me. It's not even proper English and all it seems to suggest is "angry people could get together and try to sue you". It hardly looks like a binding and enforceable legal contract (because God knows I've signed one or two in my time and they're usually dense, complex docs filled with incomprehensible legalese).
If that IS the extent of the creators "legal obligation", it reads pretty much like "Dude - seriously. You should REALLY try to give people what you promised them". ;)
I could be wrong, though.