Hey, Brad. Great questions!
Yes, I could find the data for what the 38% percent paid for the album. The average price paid by the 38% was $6 globally and $8.05 for Americans. But if you include the 62%, you get $2.26 on an average, globally, and $3.23 from Americans.
For your second question, I think it is more about the trust you have in your music and your fans than the trust in this "model." This is not a model that can work for everybody. If the public opinion is that your music is bad, no one will take it, even for free which is an embarrassment.
Were Radiohead worried about this? Yes. They felt it could end up in them looking foolish. It worked for them because they're, well, they're Radiohead.
Also, since, unlike 2007, you can stream music from so many platforms like Spotify anyway, maybe artists don't see the point of expecting many people to buy albums.
I hope this answers your questions. Have a great day!