Apparently Kickstarter's terms do state that project creators are legally responsible for fulfilling their pledge rewards, though. If those aren't fulfilled, then backers are entitled to refunds from the project creator (at least as far as Kickstarter is concerned).
This seems to be meant to give some legal pressure on project creators without punishing them too much if their projects fail for whatever reason. It's interesting though that many projects (like this one) promise rewards that explicitly require the completion of their project, in effect making them completely liable for refunds.
This is a great point. Leaving aside the practical issues of getting money from people who don't have it, this really raises some red flags about the Kickstarter model. Unless it's just a way of raising capital up-front for a fairly ho-hum project that basically just requires time and energy (and, even then, stuff can still happen). But Kickstarting projects of the sort that routinely fail a decent percentage of the time, like video games, looks a lot less attractive if the received funds look something more like a loan than an equity investment.
This seems to be meant to give some legal pressure on project creators without punishing them too much if their projects fail for whatever reason. It's interesting though that many projects (like this one) promise rewards that explicitly require the completion of their project, in effect making them completely liable for refunds.