Last year Amazon removed the 'download & transfer via USB' feature which allowed old, wifi-less Kindles to get new books onto them.
Earlier this year, Amazon 'ended support' for older (perfectly working) Kindles. What they mean by 'ending support' is remotely blocking those models from downloading new books via the Kindle Store.
Essentially, all of those older Kindles are paperweights now, unless jailbroken. As time goes on, Amazon will most likely take the same steps with more models.