Ah okay. I'll try to explain as best I understand ... hopefully I end up making some sense.
The free demo is pretty much what the game exists as - at the minute.
Although it might advance from this (free-version, that is), I'm not sure too much, as I am one of the people who have paid to test the game, and it doesn't really affect me so I haven't paid a lot of attention.
FROM THIS POINT ONWARDS new content will be added. This content will take the form of whatever it is that is needed to make the game into what it needs to be (NPCs, skills, perks, assault rifles, disease, suicide, cannibalism, extra districts etc.)
So really at this point, the person who hasn't paid and the person who has - sees no difference in the experience. And this is by design.
Anybody who has already bought the game up to this point is basically helping the Indiestone to pay their food / electricity bills - not really buying anything of any value game-wise (if you view value in terms of 'money for tangible assets' - because people can access the free demo content at this point anyway). My personal view is if you don't give money to these people, these games don't get made, so there's never the quality product to buy at the end of the day anyway.
As development continues apace, it will undoubtedly become very clear what you are actually 'buying', as you get to do all the cool stuff the future of the game is promising which you can't do in the demo.
Anybody who is pirating the game - well thats not really seen as anything worth worrying about, as content creation and bug-fixing > DRM (which will inevitably get cracked anyway). That was at least, up until a pirate version started actively taking real money from the devs (and not just 'potential' money).
And yeah, paying for the preorder was a way round the donate thing.