Well I guess they -could- make a method of getting the kickstarter being that of, well, being an option when you pay for the subscription. You can already pick how many months, etc- can't see why they couldn't do the same for the kickstarter?
The way I see it- the Dev's presumably have their own ideas- perhaps there are forces in play that we aren't aware of, such as only having one deployment method which is exclusive to Amazon US- I haven't got a clue. Though I would, personally, consider it a bit "odd", at the least, having Amazon as a distributor for -any- kind of kickstarter offer- it should be based solely through the Dev's own channels.
Look at some of the other MMO's out there (as examples)- Star Wars the Old Republic- you paid for and got your content exclusively through their website and control. Same for Mechwarrior Online- exclusively through their website and controls- I may not be new to MMO's, but I'm certainly new to the idea of letting Amazon handle your "special player content" transactions.
If nothing else- it alienates non-US customers- not just because it's US-only (technically, as we've seen from the workaround it -is- possible) but also alienates those of us without Credit Cards. No disrespect, but I haven't and never -will- own a credit card, they're time bombs for Debt- UK players alone are, at best, going to possibly have a Visa, but most have Direct Debit cards or use Paypal.
Honestly, I just hope this whole thing gets sorted. I really want the Kickstarter offer, I love the game and I'm happy to support the Devs- after all, everyone makes mistakes or doesn't forsee potential problems. I'm not saying they're idiots, they must have had their reasons. But it is an inconvenience for those of us who badly want it. The whole Steam Greenlight thing has made issues worse, if anything, as more and more non-US customers will want it and not be able to get it.
Give them time, they'll sort it. I'm sure they don't want to miss out on all the revenus from outside the US, if nothing else!