Am I missing something here? I'm sure I've seen several UK-based Kickstarter projects...

It's my understanding that the Amazon payment system used by Kickstarter for those setting up projects was only available for US bank accounts. If a UK based project was following a startup business model they could probably relatively easily find someone to facilitate this for them. If on the other hand they're self publishing a comic book (for example) they're less likely to have that kind of support. I haven't checked but either the Amazon system's changed or there's going to be an alternative payment receiving solution for non US Kickstarters.

Seems you're right! Investigated the official line on Kickstarter and found this:

The mechanics of Kickstarter (all-or-nothing funding, rewards, etc.) are identical for US and UK projects. When pledging, however, backers of UK projects will enter their payment information directly on Kickstarter rather than through Amazon Payments. All pledges will be processed securely through a third-party payments processor.