I understand that with a traditional online store, a customer could upload the downloaded file as a torrent and share it on Facebook, however, the ease of sharing a link compared to creating a torrent is pretty large.
I guess the idea is to use this for content that you never really expected to make much money from, so if it is shared you are okay with that.
I almost feel like the service should have a pay what you want option. Some people may use the stolen free link if the only pay option is $10 but would be willing to pay $5 if it was an option.