There is a lot more risk involved in backing a project where the creator has no intention on doing anything to bring the project into reality, and merely posted the project to make mad amounts of cash to walk away with.
The intention of these rules seems to be for there to be no "time machine" or "personal compact size pocket nuclear reactor" projects for fools to fall for, to pad the pockets of scammers.
By being required to actually do some work, show what you did with the money, and take the project as far as you can go with it, as far as the money will allow, it is supposed to lessen the risk of backers falling for a con.
And to force creators to be a bit more realistic with project goals, not to make promises they are not sure they can keep. At the same time, they are trying to keep Kickstarter from becoming the place where creators bring their far fetched dreams. If the only thing standing between your project and completion is money, then it's a lot more realistic than lofty dreams that no matter how much cash is thrown at you, you'll never be able to make it a reality.
How they plan on enforcing these rules on scammers that will attempt to walk away with the money, any way, I have no idea. I seriously doubt the threat of a lawsuit is going to scare scammers, since they aren't even afraid of a threat of jail time for their criminal activities.