It's the fact that it's a donation, not the pre-purchase of a physical good, that makes it so.
If you're selling a physical good, you're supposed to deliver or ship it at the time of the transaction.
> where'd you hear that whopper?
Originally from our banker at Chase that handled our merchant account set up, but it's easy enough to confirm if you look:
http://usa.visa.com/download/merchants/card-acceptance-guide...
http://www.consumer.ftc.gov/articles/0221-billed-merchandise...
> You really think Amazon Payments would have let Kickstarter go this long if they weren't kosher?
It's worth noting that even though Kickstarter is kosher, the area is gray enough that Amazon is not taking on any more Kickstarter-type sites until further notice precisely because of their legal concerns.