>Every site could set their own price, or specific tiers, which users can agree to, just like they do with subscription-based content today.

you're describing the model of a product called blendle, a service which i loved but which totally failed. they failed to attract users, and they failed to attract publishers. this isn't some new idea that nobody had tried. it's been done. and it failed, not just for blendle. people have tried micropayments, they've tried subscriptions, if you can imagine a PPV model, it's probably been tried. readers and publishers both hate it.