In the same way that Twitter is "just a database of SMS messages", Kickstarter is just a "payment checkout" - but of course they are both greater than the sum of their parts.
Their execution isn't that hard to compete with, it can be commoditized with enough resources, and for someone with actual fame I don't think they increase the amount raised by much.
If not Whedon, think Lady Gaga or JK Rowling. What would Kickstarter offer them that some private white label processing service couldn't copy?
Seems to me that for someone who doesn't already have a large fan base, a Kickstarter campaign could easily increase their take by a factor of 4 (if not 10 or 100 or 1000). For someone well-known like Whedon the factor will be smaller, but if it's 1.5 or even 1.2, the 5% fee is more than covered.