The books that go for around $10 are new releases for the most part. Older books are around $2 to $3, and most classics are free. Even if you can’t find them on Amazon, you can go to www.gutenberg.org and download the .txt versions of old works for free, move them over to the Kindle, and start enjoying them right away.
I did that with “Consolation of Philosophy”. Yes, it was the first item I put on my Kindle. :)
And there have always been people with plenty of money who don't mind dropping into Barnes and Noble to plunk down $25 or $30 for hardcopy editions of new releases, who probably find ten dollar e-books a bargain. It's just that those weighty tomes don't easily lend themselves to copying, and e-books might just be more vulnerable.
My prediction is that the freebie books will make up a very large proportion of e-books on people's devices as long as new releases are in the ten dollar range. At least if we're talking about legal copies.