They're making less per game than they would charging a lousy buck on the appstore. Given all the ways they can make whole dollars, as in plural, per purchase I'd say it's not better than 0% at all.
It's the same with Frictional Games (creators of Penumbra) and the game that they're funding through preorders, Amnesia.
They're not making more they're just selling more.
Read the attached article, it's their response to their sale: http://2dboy.com/2009/10/19/birthday-sale-results/
But relative to other models the "pay what you want" is a terrible failure - any of those games could have singlehandedly grossed $30,000 to $60,000 from the number of sales they've had today, and that's going to lose a big chunk to advertising but still make them a lot more than $1.66 a sale.
Appstore-like pricing is the exception, not the rule.
That some of the 6000 purchasers today would not pay $20 is irrelevant, others would and others from the remaining millions of game players would too.
You also disregard that I already factored in a 50% - 75% discount - the prices I put assumed a $5 - $10 price on sale.
Cheers.