Update: According to commenters on Amazon, this message was sent out from the company's customer service department:
The Kindle edition books Animal Farm by George Orwell. Published by MobileReference (mobi) & Nineteen Eighty-Four (1984) by George Orwell. Published by MobileReference (mobi) were removed from the Kindle store and are no longer available for purchase. When this occured, your purchases were automatically refunded. You can still locate the books in the Kindle store, but each has a status of not yet available. Although a rarity, publishers can decide to pull their content from the Kindle store.
It's one thing to simply remove an item from the Kindle store if a publisher changes their mind about selling kindle versions, but it's another thing entirely to delete all copies that were sold.
At the time they were bought, they had an agreement to sell them. They were legal copies, in every way. Just because someone changes their mind about how they are distributed, does NOT mean that all copies that were sold are removed from legitimate purchases.
Illegal Ayn Rand books are one thing, simple changes of mind are something totally different.
Amazon stepped WAY out of line on this one.