I understand your point, but there are only X number of seats in an airplane, airline seats are physical products. Why should the same be applicable to a digital product? I mean, it is their property so they are free to charge whatever they want (just like the users are free to leave) but it feels way more intrusive to track users' reading habits and tailor pricing to each user than saying "only 2 seats are left but 5 people are interested, so we're jacking up the price"