This is actually one psychological driver for piracy — people who have paid for a book resent being expected to pay for it again due to an arbitrary-seeming lock-in onto an aging piece of hardware. From their point of view, honesty is being punished.
There is no guarantee that B&N will stay in business, or that Amazon won’t discontinue support for older Kindle files, in the not too distant future. This is something that the hardcore readers cannot help but be aware of, because it has already bitten them in the past, if they bought a Zune, or a Palm Pilot, or any number of other devices.
