If Kickstarter deducts in advance and refunds later for a failed campaign, then it must do two credit card transactions: once to charge the money, and another to refund it. Additionally, refunds are sometimes more expensive than charges.
Not only that, but Kickstarter would also have to worry about situations like, e.g., Alice pledges money, and then later closes her card account. How would Kickstarter get the money back to Alice?
So it's almost certainly done for reasons of simplicity and avoiding legal/ethical obligations about safeguarding the money in escrow.
Except those that only come to Kickstarter to back a specific campaign, instead of backing lots.
This is why when you order things online, your credit card is typically not charged (i.e. Apple pre-orders) until your item has shipped.
IANAL so I don't know how certain things work such as Tesla deposits (what did they "ship" to you for $2,500?) and so on. But I've heard this is why Kickstarter can't do this directly.
I'm sure there are ways around it, but something to keep in mind.
The receiver will have to pay income taxes on the donations; and the giver will not be able to deduct the donation on their own income taxes. That's what requires special status.
This actually makes me realize I never thought about how people have to pay income tax on what they receive via kickstarter; I can't think of any reason they wouldn't. http://www.kickstarter.com/help/taxes