"What if you fail to reach the funding target?
We appreciate every bit of support we receive during the 30 days, and every backer will be welcomed into the Ubuntu community. If we don’t reach our target then we will focus only on commercially available handsets and there will not be an Ubuntu Edge. All contributions will be fully refunded."
This could cost indiegogo a lot.
No one wants to be the guy who stuck $700 down for something that will never exist because they were the only ones to pledge.
If it weren't for the fixed model, they would struggle to get even a fraction of the money they've raised so far.
It would be a disaster for them if they got into a position were they had costs of $1500 per phone and had to choose between bailing out or eat the losses.