You get the duramat in the retail box, originally it was just going to be for
KS backers but they decided afterwards that it could go in the retail box as well.
The
KS exclusives you will not be able to get other than through the mantic points system.
Other than that you will be able to buy it all at retail (eventually).
The main difference between buying the retail stuff and buying in via Kickstarter is that Kickstarter backers got around 70% discount off RRP once everything is added up.
The only thing being released in December is the first 5000 retail boxes with a metal survivor mini included, after that, nothing will be released for retail until Feb 2014.
KS backers will get a lot of stuff 3-6 months before retail.
Check the first post in the deadzone kickstarter thread to see all the kickstarter freebies that were included in strike team pledges, I've laid it all out there, $436 worth of stuff for $150, whereas the retail box will be $90 worth of stuff for $90:
http://www.dakkadakka.com/dakkaforum/posts/list/516236.page
And *that* is why people get in on Mantic Kickstarters. Even if you decide don't want the game, making a profit out of ebay reselling is a relatively simple task.