Google has developed this pass, and sell about $15 billion or so of it a year, with roughly $10 billion of that distributed to publishers. (Pulling numbers from memory -- check their quarterlies for the up-to-date ones.) The genius was denominating the end-user price in attention, which doesn't require a credit card number to transact in (single-click transactions, no information required, and no penny gap -- whee!), and then selling attention of desirable users to advertisers for substantial amounts of money.

Given the substantial success of Google at doing this, any micropayments system doesn't just have to clear the "Will this be better than putting up a paywall?" hurdle for every site it signs up, it also has to clear "Is this better than the largest, most entrenched, most locked-in, most supported, most widely distributed economic engine on the Internet?"