It's the micropayments problem. That "inflated fee" would have to be over a dollar to cover the costs of doing the transaction; possibly several dollars. Not only are there the costs associated with the payment, but also the additional code infrastructure, dealing with complaints, excruciating security, etc.
As you say, it would likely cost as much as the dead-tree edition, and how much usage would it get? What fraction of people would ever use it? I suspect a lot of people would say, "I could see giving you $.05 or $.25 for this, but I'm not going to pay $3.00 to read one article. And I don't want access to more than that; I just want this article."
I mean, it would probably be worth the experiment for some major newspaper or magazine. I bet somebody has tried. But the history of micropayments is already a long string of failed attempts. Money just makes everything hard, and there seems to be a minimum below which it's just not worth it.
