The thing about built-in lights for E-ink readers is that it plays merry hell with battery life and screws up the advertised lifetimes (even though it's a little unfair to the company
). Consumers are just going to see the final results - Reader A(no light) gets 4 days to a charge, Reader B(with light) gets 1 day (because the consumer used the light a lot).
Companies don't like to lose the ad-wars. *shrug*