@fleshconsumed and @nunya, You don't get it at all. Free =! copyable. The experiment purposefully includes £0.00 as an option, if that was what you're willing to pay. If someone wants to build a workable model out of this, they need to know how many people are willing to buy the music at every price point. For instance, there are plenty of people who are able to purchase this music for £0.00, but will choose not to buy it, or pirate it.
Why the hell would you pirate this music if the artists WANT to GIVE you a license?
I'm not a big RadioHead fan, but I paid for this music. I think I paid like $3, but that's a data point that they can use. £0.00 is also a data point they can use.
Indeed, don't be a dick - if you want this music, purchase it legally at whatever price you see fit, even if its £0.00. Radiohead isn't trying to guilt you out of money. I'm sure that they're comfortable with the commercial success that they've achieved.