The fundamental nature of speculative projects is that they can fail, but nothing requires Kickstarter to be used for speculative projects, and when it is, nothing requires the rewards to be dependent on project, rather than funding, success.
To illustrate the first point, companies have used Kickstarter for projects that were essentially fully developed first, and where the Kickstarter was only to provide capital for the production run (to alleviate the risk of scaling production wrong) -- with rewards being (or including) the thing being produced. As long as the rewards offered have a production cost (not retail value) less than the support level required to earn them, this eliminates the creators risk in production of a run that includes both the rewards and additional units to be sold through whatever "regular" means are appropriate to the product (ideally, it also provides buzz through the rewards to spur sales of those additional units). From that, the company can then assess future demand and appropriately scale later production runs.
To illustrate the second point, its quite possible to do a speculative product and offer rewards related to but not dependent on the project. For a game project, for instance, you could do things like exclusive prints of concept art, etc.
If you want people to share your risk, well, there are avenues that do that -- like sale of equity. Of course, those are more heavily regulated than simple sale of goods, because its very easy for avenues where you are asking the purchaser to assume risk to be used as vehicles for fraud.
And if Kickstarter commitments aren't enforced like sales commitments, it will be as much (or more) the doom of Kickstarter as anything that would strictly enforce them -- because as soon as any uncertainty is resolved in that direction, Kickstarter will become (and become known as) as an ideal vehicle for fraud, and backing projects on Kickstarter will become the equivalent of falling for a 419 scam.