So they're probably going to sell this at $40ish retail.
I think they're aiming at a sub-$20 price point for the final game (I wouldn't be surprised by $14.99, like The Cave).
They've got some crazy math, in which they're tacking on money for the bundled documentary (~$15), backer-forum access (~$10), and who knows what else -- to arrive at that $35 figure. I guess that could change if enough people perceive the game to be worth $35, maybe that's what they're trying to do.
Up to a couple of months ago they were still offering this same backer package for $15 (which was the Kickstarter rate on that stuff). They're still giving 2Player Productions a percentage of sales.